共查询到20条相似文献,搜索用时 31 毫秒
1.
Rex E. Shepherd Thomas W. Stringfield Andrew A. Amoscato 《Inorganica chimica acta》2004,357(4):965-979
The electrospray mass spectrum (ESI-MS) of cis-[Ru(NO)Cl(bpy)2]Cl2 (bpy=2,2′-bipyridine), obtained from 50% CH3OH/50% H2O as the mobile solvent, exhibited ruthenium-containing ions derived from a {[RuII(NO+)Cl(bpy)2]2+, Cl−}+ ion pair (m/z=514) and [RuII(NO+)Cl(bpy)2]2+ (m/z=239.5). [RuIIICl(bpy)2]2+, from the loss of NO from the 239.5 ion, is detected at m/z=224.5. Only the m/z 514 ion pair is detected when 100% CH3OH mobile solvent is used, but the presence of even small amounts of water prompted the additional detection of the m/z 239.5 and m/z 224.5 ions under tandem MS-MS conditions. Ruthenium-chloro-containing ions appear as a characteristic collection of eight main, and four lesser, intense ions created from combinations 104Ru, 102Ru, 101Ru, 99Ru, 98Ru, 96Ru, 35Cl and 37Cl isotopes with minor contributions from 13C, etc. For convenience of discussion, only the most abundant m/z species are mentioned herein as representative of all the isotopically distributed ions.Four fragmentation channels are detectable from the m/z=514 chloride ion pair: (1) the loss of HCl (main channel; ca. 50% of fragmentation events), (2) the loss of NO (ca. 12% ), (3) the loss of bpy (minor pathway), and (4) the loss of Cl atom (ca. 38% ).Loss of NO from ion m/z 514 yields ion m/z 484, which is the precursor of ions m/z 448 (by loss of HCl), m/z 328 (by loss of bpy) and m/z 292 (by loss of HCl and bpy). Loss of HCl from ion m/z 514 generates ion m/z 478, [RuII(NO+)Cl(bpyH)(bpy-H)]+, deprotonated at the ortho C-H of one bpy ligand. In MS-MS experiments, the m/z 478 ion was established to undergo loss of NO, producing ion m/z 448, rejoining further fragmentation process for ion m/z 448 at this point. Loss of neutral bipyridine from m/z 514 in low yield produces ion m/z 358, which undergoes further loss of NO to form [RuCl2(bpy)]+ ion (m/z=328). MS-MS “neutral loss of 30” spectra confirmed the NO loss events as part of the fragmentation sequence for all four pathways.A fourth species of m/z=479 from the “514” ion is obtained by an internal electron transfer from Cl− of the ion pair, and loss of the resultant neutral Cl atom. The product [RuII(NO·)Cl(bpy)2]+ “479” fragment undergoes facile loss of NO to generate [RuIICl(bpy)2]+ (m/z=449). Ion m/z 449 gives rise to ions m/z 413 (loss of HCl) and m/z 257(loss of HCl and bpy). MS-MS experiments confirm the neutral loss of Cl from the m/z 514 ion, and the formation of the m/z 449 ion via m/z 479 and m/z 514 parents. This pathway was not observed in a prior study for the related complex, [Ru(NO)Cl(dpaH)(dpa−)]+ (dpaH=2,2′-dipyridylamine), which does not have an external Cl− in an ion pair. 相似文献
2.
The trpX mutation in Escherichia coli reduces trp operon attenuation in strains carrying wild-type tRNATrp. The trpX? phenotype is alleviated (attenuation is restored) in UGA-suppressor tRNATrp-carrying strains (Yanofsky &; Soll, 1977).The tRNA from various trpX? strains was characterized biochemically. Sequence analyses of wild-type tRNATrp and UGA suppressor tRNATrp, both derived from trpX? strains, reveal an unmodified A in the position (adjacent to the anticodon) normally occupied by the hypermodified base ms2i6A.In addition, several tRNAs from trpX? cells were characterized by RPC-5 column chromatography. We find that only tRNAs normally having ms2i6A exhibit altered elution profiles when compared to the homologous tRNAs from trpX? cells. Introduction of the UGA suppressor into trpX? cells does not restore normal Chromatographic behavior. These results suggest that the trpX gene product is necessary for the synthesis of ms2i6A. Thus, we propose that miaA (for the first gene involved in ms2i6A synthesis) replaces the trpX designation.The results reported here are discussed with regard to a model proposed by Lee &; Yanofsky (1977) in which efficient translation of the tandem trp codons in the leader sequence RNA is required for normal attenuation of the trp operon. 相似文献
3.
《Acta Oecologica》1999,20(2):87-92
A study was conducted to determine soil chemistry in an uncut black spruce (Picea mariana) forest with and without the ericaceous understory shrub Kalmia angustifolia, as well as on a cut black spruce forest currently dominated by Kalmia. The organic (humus) and mineral (Ae, upper and lower B horizons) soils associated with Kalmia from uncut and cut forests, and non-Kalmia soils from uncut forest, were analyzed for selected soil properties. In general, mineral soils (B horizon) associated with Kalmia in uncut forest have lower values for organic matter (3.25%), organic nitrogen (0.66 mg·g−1), Fe3+ (95.4 μg·g−1) and Mn2+ (9 μg·g−1), and higher values for pH (4.12) and Ca2+ (27 μg·g−1) compared to non-Kalmia (organic matter, 3.43%; organic-N, 1.15 mg·g−1; Fe3+, 431 μg·g−1; Mn2+, 23.2 μg·g−1; pH, 3.14; Ca2+, 15.6 μg·g−1) and cut black spruce-Kalmia (organic matter, 3.74%; organic-N, 0.94 mg·g−1; Fe3+, 379 μg·g−1; Mn2+, 27 μg·g−1; pH, 2.87; Ca2+, 25.2 μg·g−1) forest. The high C:N ratio in Kalmia mineral soil from upper B (29.73) and lower B (identified as B+) (33.08) in uncut black spruce forest was recorded compared to non-Kalmia soils in B (18.17) and B+ (17.05) horizons in uncut black spruce forest. Phenolics leached out from Kalmia litter were lower in Kalmia associated soils than the non-Kalmia soils from the uncut forest, and Kalmia associated soils from the cut forest area. Results indicate that soils associated with Kalmia were nutrient poor particularly for nitrogen, phosphorus, iron and manganese, and provide some basis for the hypothesis that Kalmia has dominated microsites that were nutrient poor prior to Kalmia colonization. 相似文献
4.
This paper concerns the likely origin of three mutations with large effects on ovulation rate identified in the Belclare and Cambridge sheep breeds; two in the BMP15 gene (FecXG and FecXB) and the third (FecGH) in GDF9. All three mutations segregate in Belclare sheep while one, FecXB, has not been found in the Cambridge. Both Belclare and Cambridge breeds are relatively recently developed composites that have common ancestry through the use of genetic material from the Finnish Landrace and Lleyn breeds. The development of both composites also involved major contributions from exceptionally prolific ewes screened from flocks in Ireland (Belclare) and Britain (Cambridge) during the 1960s. The objective of the current study was to establish the likely origin of the mutations (FecXG, FecXB and FecGH) through analysis of DNA from Finnish Landrace and Lleyn sheep, and Galway and Texel breeds which contributed to the development of the Belclare breed. Ewes with exceptionally high prolificacy (hyper-prolific ewes) in current flocks on Irish farms were identified to simulate the screening of ewes from Irish flocks in the 1960s. DNA was obtained from: prolific ewes in extant flocks of Lleyn sheep (n = 44) on the Lleyn peninsula in Wales; hyper-prolific ewes (n = 41); prolific Galway (n = 41) ewes; Finnish Landrace (n = 124) and Texel (n = 19) ewes. The FecXG mutation was identified in Lleyn but not in Finnish Landrace, Galway or Texel sheep; FecXB was only found among the hyper-prolific ewes. The FecGH mutation was identified in the sample of Lleyn sheep. It was concluded from these findings that the Lleyn breed was the most likely source of the FecXG and FecGH mutations in Belclare and Cambridge sheep and that the FecXB mutation came from the High Fertility line that was developed using prolific ewes selected from commercial flocks in Ireland in the 1960′s and subsequently used in the genesis of the Belclare. 相似文献
5.
Hua Zhang Zhenhui Wang Lei Wang Ren Mu Zhi Zou Kun Yuan Yuekun Wang Haiping Wu Juquan Jiang Lifu Yang 《Extremophiles : life under extreme conditions》2014,18(1):89-98
In this study, metagenomic DNA was screened for the Na+/H+ antiporter gene from the halophilic bacteria in Daban Salt Lake by selection in Escherichia coli KNabc lacking three major Na+/H+ antiporters. One gene designated as Hb_nhaD encoding a novel NhaD-type Na+/H+ antiporter was finally cloned. The presence of Hb_NhaD conferred tolerance of E. coli KNabc to up to 0.5 M NaCl and 0.2 M LiCl, and an alkaline pH. Hb_NhaD has the highest identity (70.6 %) with a putative NhaD-type Na+/H+ antiporter from an uncharacterized Clostridiaceae species, and also has lower identity with known NhaD-type Na+/H+ antiporters from Halomonas elongata (20.8 %), Alkalimonas amylolytica (19.0 %), Vibrio parahaemolyticus (18.9 %) and Vibrio cholerae (18.7 %). pH-dependent Na+(Li+)/H+ antiport activity was detected from everted membrane vesicles prepared from E. coli KNabc carrying Hb_nhaD. Hb_NhaD exhibited very high Na+(Li+)/H+ antiport activity over a wide pH range from 6.5 to 9.0 with the highest activity at pH 7.0 which is significantly different from those of the above known NhaD-type Na+/H+ antiporters. Also, the apparent K m values of Hb_NhaD for Na+ and Li+ at pH 7.0 were determined to be 1.31 and 2.16, respectively. Based on the above results, we proposed that Hb_NhaD should be categorized as a novel NhaD-type Na+/H+ antiporter. 相似文献
6.
J. Eric Hillerton 《Journal of insect physiology》1979,25(1):73-77
The ultimate tensile strength (σUT) and the modulus of elasticity (E) of Rhodnius extensible cuticle are σUT = 2.20 × 107 Nm?2, E = 2.43 × 108 Nm?2 (unplasticised); σUT = 1.43 × 107 Nm?2, E = 9.45 × 106 Nm?2 (plasticised with 5HT) and σUT = 9.05 × 106 Nm, E = 2.46 × 106 Nm?2 (plasticised in pH 5 buffer).The mechanical properties of cuticle from insects which have deposited additional layers of cuticle after they have been fed differ from those of cuticle from unfed insects. This is possibly due to the different composition of the additional cuticle: it is suggested that the post-feeding cuticle is providing protection and a template for the next instars cuticle.The maximum strain of extensible cuticle from starved insects is related to the amount of matrix protein present. 相似文献
7.
Cysteine synthases were partially purified from leaf tissue of 3 selenium-accumulator species (Neptunia amplexicaulis, Astragalus racemosus and A. bisulcatus) and 4 non-accumulators (peas, white clover, A. sinicus and A. hamosus). The properties of all 7 enzymes with respect to cysteine synthesis from S2? and O-acetylserine (OAS) were similar. All of the enzymes also catalysed the synthesis of selenocysteine when S2? was replaced with Se2?. There were no distinct differences between the properties of the enzymes from selenium-accumulator and non-accumulator plants with respect to selenocysteine synthesis. Se2? inhibited the synthesis of cysteine and S2? inhibited the synthesis of selenocysteine implying competition between S2? and Se2? for the enzyme. The affinities of the enzymes for Se2? were substantially greater than for S2?, and Vmax (selenocysteine) was ca 7–48% of Vmax (cysteine). Isolated pea chloroplasts catalysed the synthesis of selenocysteine from OAS and Se2? at a rate of ca 22–26 μmol/mg Chl/hr. Sonicating the chloroplasts slightly enhanced the rate. 相似文献
8.
The asymmetrical nitrosyl-deoxy hybrid haemoglobin, (αNOβNO), (αdeoxyβdeoxy), was prepared by removing oxygen with sodium dithionite from a mixture of oxyhaemoglobin and nitrosylhaemoglobin (Cassoly, 1978). This asymmetrical hybrid exhibited a distinctive triplet hyperfine structure in the electron paramagnetic resonance spectrum. This triplet has been shown to arise predominantly from the nitrosyl haem of an α subunit which has a deoxy-like structure (Nagai et al., 1978). By removing one or two carboxyl-terminal residues by carboxypeptidase digestion before mixing, one can obtain asymmetrical nitrosyl-deoxy hybrid haemoglobins in which only one of the four subunits is specifically modified. Eight such modified derivatives were examined by e.p.r.2. They were (desArgαNOβNO) (αdeoxyβdeoxy), (desArg-TyrαNOβNO) (αdeoxyβdeoxy), (αNOdesHisβNO) (αdeoxyβdeoxy), (αNOdesHis-Tyr βNO) (αdeoxyβdeoxy), (αNOβNO) (desArgαdeoxyβdeoxy), (αNOβNO) (desArg-Tyrαdeoxyβdeoxy), (αNOβNO) (αdeoxydesHisβdeoxy) and (αNOβNO) (αdeoxydesHis-Tyrβdeoxy), where desArg, desArg-Tyr, desHis and desHis-Tyr indicate that the amino acids were removed from the carboxyl terminus of the subunit.The e.p.r. spectra for these eight derivatives have a more or less reduced relative intensity of the triplet, indicating that the non-covalent bonds involving carboxyl-terminal residues which stabilize the structure of deoxyhaemoglobin (Perutz, 1970) must all be intact in the unmodified asymmetrical nitrosyl-deoxy hybrid haemoglobin, (αNOβNO) (αdeoxyβdeoxy). By comparing the relative intensity of the triplet we were able to examine the effect of modification of one specific carboxyl terminus on the nitrosyl haem in the α1 subunit. The effect was not symmetric, but increased in the order α1 < β2 < β1 < α1 (suffices 1 and 2 as defined by Perutz (1965)). We attribute this order to the non-equivalence of intersubunit interactions. 相似文献
9.
This paper describes the structure of neutral exopolysaccharide (EPS) produced by Lactobacillus johnsonii 142, strain of the lactic acid bacteria isolated from the intestine of mice with experimentally induced inflammatory bowel disease (IBD). Sugar and methylation analyses along with 1H and 13C NMR spectroscopy, including two-dimensional 1H,1H COSY, TOCSY, NOESY, and 1H,13C HSQC experiments revealed that the repeating unit of the EPS is a pentasaccharide:→3)-α-d-Galp-(1→3)-β-d-Glcp-(1→5)-β-d-Galf-(1→3)-α-d-Galp-(1→3)-α-d-Galp-(1→The rabbit antiserum raised against whole cells of L. johnsonii 142 reacted with homologous EPS, and cross-reacted with exopolysaccharide from Lactobacillus animalis/murinus 148 isolated also from mice with IBD, but not reacted with EPS of L. johnsonii 151 from healthy mice. 相似文献
10.
Alejandro M. Labella M. Dolores Castro Manuel Manchado Teresa Lucena David R. Arahal Juan J. Borrego 《Systematic and applied microbiology》2018,41(5):444-451
Three strains, H01100409BT, H01100413B, and H27100402HT, were isolated from several internal organs of diseased redbanded seabream (Pagrus auriga) reared in Andalusia (Southern Spain). All strains were studied by phenotypic, including chemotaxonomy, and genomic characteristics. Phylogenetic analysis based on concatenated sequences of six housekeeping genes (gyrB, ftsZ, topA, mreB, gapA, and 16S rRNA) supported the inclusion of the strains within the clade Phosphoreum of the genus Photobacterium, and two of the strains (H27100402HT and H01100409BT) formed a tight group separated from the closest species P. aquimaris. Genomic analyses, including average nucleotide identity (ANIb and ANIm) and DNA–DNA hybridization (DDH), clearly separated strains H27100402HT and H01100409BT from the other species within the clade Phosphoreum with values below the thresholds for species delineation. The chemotaxonomic features (including FAME analysis and MALDI-TOF-MS) of H27100402HT and H01100409BT strains confirmed their differentiation from the related taxa. The results demonstrated that strain H01100413B was classified as P. aquimaris and the strains H27100402HT and H01100409BT represented a new species each in the genus Photobacterium, for which we propose the names Photobacterium malacitanum sp. nov., type strain H27100402HT (=CECT 9190T = LMG 29992T), and Photobacterium andalusiense sp. nov., type strain H01100409BT (=CECT 9192T = LMG 29994T). 相似文献
11.
《Animal Feed Science and Technology》1998,75(1):15-25
The NIR spectra of 135 samples of the following green crop oats (Avena sativa), barley (Hordeum vulgare), triticale (x Triticosecale), wheat (Triticum durum), ryegrass (Lolium multiflorum) and sorghum (x Sorghum sudanense) grown in Portugal, were obtained by reflectance from oven-dried, milled whole plant material. Samples were cut at various stages of development (viz. stem elongation, boot, early heading, milk and dough stage) and were analysed by standard laboratory methods. The nutritive value was evaluated in vivo using rams in metabolic cages. The green crops showed values of ASH varying from 5.5 to 14.9%, crude protein (CP) from 5.0 to 22.3%, crude fibre (CF) from 25.3 to 40.4%, neutral detergent fibre (NDF) from 45.9 to 77.2%, acid detergent fibre (ADF) from 23.6 to 49.9%, acid detergent lignin (ADL) from 1.7 to 8.0%, dry matter digestibility (DMD) from 53.2 to 82.9%, organic matter digestibility (OMD) from 56.2 to 85.0% and dry matter intake (IVDMI) from 35.8 to 88.6 g DM kg−1 W0.75. Spectra were used to develop NIR calibration models for ASH (SEC=0.72; r2=0.90), CP (SEC=0.63; r2=0.98), CF (SEC=1.02; r2=0.94), NDF (SEC=1.41; r2=0.97), ADF (SEC=1.43; r2=0.96), ADL (SEC=0.49; r2=0.87) and in vivo attributes DMD (SEC=2.61; r2=0.86), OMD (SEC=2.36; r2=0.88) and IVDMI (SEC=6.05; r2=0.41). Calibration models were successful for all parameters except for IVDMI. However, animal attributes were less successfully predicted than chemical composition. Calibration models were generated omitting one of the six plant species to assess their ability to accommodate unknown green crop species not represented in the calibration model. In general, NIRS was shown to provide acceptable prediction of composition across different species of green crop cereals whether or not these were included in the calibration process. 相似文献
12.
The improved methods for the preparation of valency hybrid hemoglobins, (α3+β2+)2 and (α2+β3+)2 were presented. The (α3+β2+)2 valency hybrid was separated from the solutions of partially reduced methemoglobin with ascorbic acid, by using CM 32 column chromatography. The (α2+β3+)2 valency hybrid was also isolated from hemoglobin solutions, which were partially oxidized with ferricyanide, by chromatography on CM 32 column. These valency hybrid hemoglobins were found to be single on isoelectric focusing electrophoresis. Present procedures are very simple and are suitable for the bulk preparation of (α3+β2+)2 and (α2+β3+)2 valency hybrids. 相似文献
13.
Yue Shen Chongxi Liu Xiangjing Wang Junwei Zhao Feiyu Jia Yuqin Zhang Liang Wang Deguang Yang Wensheng Xiang 《Antonie van Leeuwenhoek》2013,103(2):293-298
A novel actinomycete, designated strain NEAU-M9T, was isolated from soybean root (Glycine max (L.) Merr) and characterized using a polyphasic approach. 16S rRNA gene sequence similarity studies showed that strain NEAU-M9T belonged to the genus Actinoplanes, being most closely related to Actinoplanes campanulatus DSM 43148T (98.85 %), Actinoplanes capillaceus DSM 44859T (98.70 %), Actinoplanes lobatus DSM 43150T (98.30 %), Actinoplanes auranticolor DSM 43031T (98.23 %) and Actinoplanes sichuanensis 03-723T (98.06 %); similarity to other type strains of the genus Actinoplanes ranged from 95.87 to 97.56 %. The neighbour-joining phylogenetic tree based on 16S rRNA gene sequences showed that the isolate formed a distinct phyletic line with A. campanulatus DSM 43148T and A. capillaceus DSM 44859T. This branching pattern was also supported by the tree constructed with the maximum-likelihood method. However, the low level of DNA–DNA relatedness allowed the isolate to be differentiated from the above-mentioned two Actinoplanes species. Moreover, strain NEAU-M9T could also be distinguished from the most closely related species by morphological, physiological and characteristics. Therefore, it is proposed that strain NEAU-M9T represents a novel Actinoplanes species, Actinoplanes hulinensis sp. nov. The type strain of Actinoplanes hulinensis is NEAU-M9T (= CGMCC 4.7036T = DSM 45728T). 相似文献
14.
The hybridization kinetics of poly(A)+-RNA preparations from the cotyledons of developing pea (Pisum sativum seeds to complementary DNAs have shown that the number of distinct sequences in poly(A)+ -RNA decreases from ca 20 000 at the early stage of cotyledon development to ca 200 at a late stage of cotyledon development. The decrease in sequences is accounted for entirely by the disappearance of ‘rare’ poly(A)+ -RNAs (< 103 copies/cell) as seed development proceeds. There is an increase (1–6) in very abundant poly(A)+-RNA sequences (? 5 × 105 copies/cell) from early- to mid-developmental stages, concomitantly with the increase in the synthesis of seed-specific storage protein polypeptides. In agreement with the continuing synthesis of most of these polypeptides to the end of seed development, the number of very abundant poly(A)+-RNAs is maintained to the late cotyledon development stage. Abundant poly(A)+-RNA sequences (ca 104 sequences/cell) increase from 80 to 180 during development, possibly corresponding to the polypeptides which are not storage proteins but are known to be accumulated in pea seeds. Hybridization of single-copy pea genomic DNA sequences to poly(A)+-RNA from developing seeds showed that ca 5 % of the single-copy sequences were present in mRNA from mid-development cotyledons. In addition, hybridization of cDNA prepared against poly(A)+-RNA from nuclei of early development cotyledons to the corresponding cytoplasmic polysomal poly(A)+-RNA showed that the cytoplasmic poly(A)+-RNA contained ca 50 % of the sequences present in the nuclei. These results are discussed and interpreted in the light of existing results from similar systems. 相似文献
15.
Rangasamy Anandham Pandiyan Indira Gandhi Soon Wo Kwon Tong Min Sa Yong Ki Kim Hyeong Jin Jee 《Archives of microbiology》2009,191(12):885-894
A thiosulfate-oxidizing facultative chemolithoautotrophic Burkholderia sp. strain ATSB13T was previously isolated from rhizosphere soil of tobacco plant. Strain ATSB13T was aerobic, Gram-staining-negative, rod shaped and motile by means of sub-terminal flagellum. Strain ATSB13T exhibited mixotrophic growth in a medium containing thiosulfate plus acetate. A phylogenetic study based on 16S rRNA gene sequence analysis indicated that strain ATSB13T was most closely related to Burkholderia kururiensis KP23T (98.7%), Burkholderia tuberum STM678T (96.5%) and Burkholderia phymatum STM815T (96.4%). Chemotaxonomic data [G+C 64.0 mol%, major fatty acids, C18:1 ω7c (28.22%), C16:1 ω7c/15 iso 2OH (15.15%), and C16:0 (14.91%) and Q-8 as predominant respiratory ubiquinone] supported the affiliation of the strain ATSB13T within the genus Burkholderia. Though the strain ATSB13T shared high 16S rRNA gene sequence similarity with the type strain of B. kururiensis but considerably distant from the latter in terms of several phenotypic and chemotaxonomic characteristics. DNA–DNA hybridization between strain ATSB13T and B. kururiensis KP23T was 100%, and hence, it is inferred that strain ATSB13T is a member of B. kururiensis. On the basis of data obtained from this study, we propose that B. kururiensis be subdivided into B. kururiensis subsp. kururiensis subsp. nov. (type strain KP23T = JCM 10599T = DSM 13646T) and B. kururiensis subsp. thiooxydans subsp. nov. (type strain ATSB13T = KACC 12758T). 相似文献
16.
Hubert L. Dulieu 《Mutation research》1974,25(3):289-304
A greenish-yellow mutant was obtained after treatment of seeds of Nicotiana tabacum L. var. Xanthi n.c. with ethyl methanesulfonate (EMS). Two genetically independent mutations (a1 and a2) were isolated. The first mutation (a1) antagonizes the function of its partially dominant a1+ allele. The second mutation (a2) is amorphous but strongly interacts with a1.Among the nine possible genotypes at the two loci, five varied in somatic cells. The heterozygous state a1+/a1 strongly increased the frequency of both spontaneous and induced variations. However, two homozygotes also showed variations.Variants were isolated from induced and spontaneous non-reciprocal and reciprocal variations within paliside tissues by bud induction in vitro. They were genetically tested. In this first paper, only non-reciprocal variations are reported.Green variants from the greenish-yellow (J1) dihybrid a1+/a1a2+/a2 clone had two genotypes: the first was due to true reversions of a1 to a1+, whereas the second was due to amorphous a10 mutations from a1. These a10 mutations may well be deletions.The lightest yellow variants from J1 were due to mutations either from a1+ into a1 or from a2+ into a2.Deletions at the a1+?a1 locus led to either yellow variations when a1+ was lost, or to false reversions when the antagonistic allele a1 was lost.Amorphous alleles at the a1+?a1 locus were also isolated from tissues other than J+. They gave zygotic lethality (s) that probably varied with the size of the deletions. Thus, true reversions and deletions at the a1+?a1 locus could be distinguished from one another by progeny tests.Other variants showed higher frequencies of spontaneous variations (instability). Somatic changes observed in these unstable systems were due to modifications at the marker loci. The genetic nature of this instability is not yet known.There is strong evidence that the genetic events involved in these non-reciprocal variations were deletions, conversions and point mutations. True reversions from a1 into a1+ and new mutations from a1+ into a1 were obtained only from a1+/a1. It was therefore supposed that the changes observed took place only in heterozygotes, and the conversion hypothesis was made. Attempts are being made to prove that conversions do exist in higher plants, and to find out if this process, as deletions, is induced by radiation. 相似文献
17.
18.
Ramette A Frapolli M Fischer-Le Saux M Gruffaz C Meyer JM Défago G Sutra L Moënne-Loccoz Y 《Systematic and applied microbiology》2011,34(3):180-188
Fluorescent Pseudomonas strains producing the antimicrobial secondary metabolite 2,4-diacetylphloroglucinol (Phl) play a prominent role in the biocontrol of plant diseases. A subset of Phl-producing fluorescent Pseudomonas strains, which can additionally synthesize the antimicrobial compound pyoluteorin (Plt), appears to cluster separately from other fluorescent Pseudomonas spp. based on 16S rRNA gene analysis and shares at most 98.4% 16S rRNA gene sequence identity with any other Pseudomonas species. In this study, a polyphasic approach based on molecular and phenotypic methods was used to clarify the taxonomy of representative Phl+ Plt+ strains isolated from tobacco, cotton or wheat on different continents. Phl+ Plt+ strains clustered separately from their nearest phylogenetic neighbors (i.e. species from the ‘P. syringae’, ‘P. fluorescens’ and ‘P. chlororaphis’ species complexes) based on rpoB, rpoD or gyrB phylogenies. DNA-DNA hybridization experiments clarified that Phl+ Plt+ strains formed a tight genomospecies that was distinct from P. syringae, P. fluorescens, or P. chlororaphis type strains. Within Phl+ strains, the Phl+ Plt+ strains were differentiated from other biocontrol fluorescent Pseudomonas strains that produced Phl but not Plt, based on phenotypic and molecular data. Discriminative phenotypic characters were also identified by numerical taxonomic analysis and siderotyping. Altogether, this polyphasic approach supported the conclusion that Phl+ Plt+ fluorescent Pseudomonas strains belonged to a novel species for which the name Pseudomonas protegens is proposed, with CHA0T (=CFBP 6595T, =DSM 19095T) as the type strain. 相似文献
19.
《Biochimica et Biophysica Acta (BBA)/Lipids and Lipid Metabolism》1996,1299(2):235-244
The products of desaturation and elongation of [1−14C] 18:3(n − 3) and [1−14C]20:5(n − 3) were studied using hepatocytes and microsomes prepared from livers of trout maintained on diets containing either olive oil or fish oil, to establish the extent to which the formation of 22:6(n − 3) was enhanced in the absence of dietary 22:6(n − 3) and to investigate the pathway(s) of conversion of 18:3(n − 3) and 20:5(n − 3) to 22:6(n − 3). Levels of 20:5(n − 3) and 22:6(n − 3) in the total lipid of hepatocytes from trout fed olive oil were 20-fold and 10-fold, respectively, lower than in cells from trout fed fish oil. For both dietary groups, [1−14C]18:3(n − 3) was incorporated into hepatocyte lipid to a greater extent than [1−14C]20:5(n − 3). Almost 70% of the total radioactivity from [1−14C]18:3(n − 3) was recovered in hepatocyte triacylglycerols, whereas radioactivity from [1−14C]20:5(n − 3) was recovered almost equally in neutral lipids (52%) and polar lipids (48%). The products of desaturation and elongation from both labelled substrates were esterified mainly into hepatocyte polar lipids, whereas elongation products of [1−14C]18:3(n − 3) were preferentially incorporated into neutral lipids. Radioactivity recovered in the 22:6(n − 3) of polar lipids of hepatocytes from trout fed olive oil, from both 14C substrates, was approximately double that in hepatocytes from trout fed fish oil. No radioactivity from either [1−14C]18:3(n − 3) or [1−14C]20:5(n − 3) was incorporated into 22:6(n − 3) by microsomes isolated from livers from either group of fish and incubated in the presence of acetyl-CoA, malonyl-CoA, NADH, NADPH, ATP and coenzyme A. However, significant radioactivity was recovered in 24:5(n − 3) and 24:6(n − 3) from [1−14C]20:5(n − 3) and more radioactive 24:6(n − 3) accumulated in microsomes from trout fed olive oil than from trout fed fish oil. The results establish that the formation of 22:6(n − 3) from both 18:3(n − 3) and 20:5(n − 3) in hepatocytes of rainbow trout is stimulated by omitting 22:6(n − 3) from the diet and are consistent with the biosynthesis of 22:6(n − 3) in trout liver cells proceeding via 24:5(n − 3) and 24:6(n − 3) intermediates. 相似文献
20.
Coupling with Packaging Explains Apparent Nonreciprocality of Chi-Stimulated Recombination of Bacteriophage Lambda by Reca and Recbc Functions 总被引:10,自引:5,他引:5
Ichizo Kobayashi Mary M. Stahl Frederic R. Fairfield Franklin W. Stahl 《Genetics》1984,108(4):773-794
Chi (χ, 5'-GCTGGTGG) is a recombinator in RecA- and RecBC-mediated recombination in Escherichia coli. In vegetative recombination between two bacteriophage lambda strains, one with and the other without Chi (a+χ+b- x a-χob+), the χ-containing recombinant (a-χ+b -) is less abundant than the non-χ-containing recombinant (a+χob+). Previously this was taken was evidence for nonreciprocality of χ-stimulated exchange. This inequality, however, is now seen to result from an event at cos (λ's packaging origin) that both activates Chi and initiates DNA packaging. An event at rightward cos leads to activation of leftward χ on the same chromosome for an exchange to its left. From the resulting circulating dimer (—cos-a+-χo-b +-cos-a --χ+-b-—), the cos that activated χ is more likely to be used for rightward packaging initiation than is the cos from the other parent. Consistent with this coupling model is "biased packaging" in λ carrying two cos sites per monomer genome. When their maturation is dependent on dimerization by χ-stimulated exchange, the phage particles result more often from packaging from the cos that activates χ than from packaging from the other cos. Since Chi activation and packaging can be uncoupled, we infer that some early and reversible step in packaging activates χ. A strong candidate for this step is a double-strand break at cos that provides an oriented entry site for a recombinase. 相似文献