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1.
Summary A general method has been developed for the deletion of restriction endonuclease sites in bacterial plasmid DNA. The procedure involves partial digestion of the covalently closed circular plasmid DNA with an appropriate restriction endonuclease under conditions which allow accumulation of unit-length linear DNA molecules, controlled digestion of the exposed 5 ends with the 5-exonuclease, and in vivo recircularization of the resulting linear DNA in a bacterial host cell. The method has been used for the deletion of one of the two EcoRI sites in the plasmid pML2 (colE1-Km). Two of the resulting plasmids, pCR1 and pCR11, have a single EcoRI cleavage site, but retain genetic determinants specifying resistance to colicin E1 and kanamycin, and thus may be useful as vectors for the cloning and amplification of DNA in bacteria. 相似文献
2.
Mark W. Lubbers Lawrence J. H. Ward Tom P. J. Beresford Brion D. W. Jarvis Audrey W. Jarvis 《Molecular & general genetics : MGG》1994,245(2):160-166
The cohesive termini of the DNA genome of the lactococcal bacteriophage c2 were directly sequenced and appeared to be complementary, non-symmetrical, 9-nucleotide single-stranded, 3 extended DNAs, with the following sequence: 5-GTTAGGCTT-3 3-CAATCCGAA-5. DNA located on either side of the cohesive ends was sequenced and several repeats and a region with the potential for a DNA bend were found. Previously sequenced cos regions of 13 other bacteriophages were also examined for similar sequence features. All of the bacteriophages from gram-positive hosts had 3 extended DNA termini, in contrast to the bacteriophages from gram-negative hosts, which had 5 extended DNA termini. All bacteriophages had a region of dyad symmetry close to the cohesive termini. A 7.3 kb DNA fragment of the c2 genome containing the cos sequences was cloned; transduction experiments demonstrated that these cloned sequences could act as a substrate for packaging enzymes of phage c2. 相似文献
3.
Kojic Snezana Todorovic Vesna Ristic Dejan Savic Ana Stefanovic Dragana 《Molecular and cellular biochemistry》1998,189(1-2):207-212
Three Drosophila embryonic deoxyribonucleases, designated den1, den2 and den3, are identified in nuclear extracts separated by glycerol density gradient centrifugation. Den1, removes short products from the 5-ends of single-stranded DNA or double-stranded DNA with either blunt or 5-recessed termini. Den2 is inactive with single-stranded DNA and acts as 3-exonuclease with double-stranded DNA possessing either blunt or 3-recessed termini. Den3 preferentially uses partial duplex DNA containing single-stranded gap and it catalyzes hydrolysis, in 3-5 direction, of one of the shorter strands that flank the gap. Nucleolytic activities of den1, den2 and den3 are inhibited with ATP. 相似文献
4.
Identification of a codominant amplified polymorphic DNA marker linked to the verticillium wilt resistance gene in tomato 总被引:3,自引:0,他引:3
L. M. Kawchuk D. R. Lynch J. Hachey P. S. Bains F. Kulcsar 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1994,89(6):661-664
Resistance to verticillium wilt, a vascular disease causing yield losses in many crops, is conferred in tomato by a single dominant allele, Ve. A population segregating for the Ve allele was generated using near-isogenic tomato lines. Analysis of the parental tomato DNA using the polymerase chain reaction and 400 random primers, each 10 deoxyribonucleotides in length, produced 1,880 amplified DNA fragments. Of the four polymorphisms observed between the resistant and susceptible parental genotypes, only one was linked to the Ve gene. No recombination was observed between this DNA marker and the Ve locus, indicating that the linkage is less than 3.5±2.7 cM. The marker detected both the susceptible and resistant alleles, producing amplified DNA fragments of approximately 1,300 and 1,350 bp, respectively. The sequence of the primer, determined from cloned amplified products, was 5 CTCACATGCA 3 instead of the expected 5 CTCACATGCC 3. The marker will be of value to tomato breeding programs because of the tight linkage, Codominant nature, and analytical procedure utilized. 相似文献
5.
Rachel Galun 《Entomologia Experimentalis et Applicata》1989,50(2):133-139
Females of the medfly, Ceratitis capitata, prefer sucrose solutions containing ribonucleotides to sucrose solutions without them. The order of preference for the nucleotides was: 5GMP>GTP>5CMP>5IMP >dGMP>5UMP>5AMP>5XMP=ATP=2 & 3GMP=RP>3AMP.2AMP, guanosine, inosine, adenine and 5TMP produced no significant stimulation. Females sterilized by irradiation showed reduced attraction to 5GMP as compared to non-irradiated females.Optimal molecular configuration for phagostimulation includes: phosphorylation at the 5 position of the ribose, free hydroxyl groups at 2 and 3 on the ribose, and an NH2 group at the 2 position of the aromatic ring of purine.It is proposed that the 5GMP in yeast hydrolyzate can be used as a measure of the suitability of the hydrolyzate as a bait.
Abbreviations 5AMP Adenosine 5-monophosphate - 3AMP Adenosine 3-monophosphate - 2AMP Adenosine 2-monophosphate - dAMP 2-deoxyadenosine 5-monophosphate - ADP Adenosine 5-diphosphate - ATP Adenosine 5-triphosphate - 5GMP Guanosine 5-monophosphate - 2GMP Guanosine 2-monophosphate - 3GMP Guanosine 3-monophosphate - dGMP 2-deoxyguanosine 5-monophosphate - GDP Guanosine 5-diphosphate - GTP Guanosine 5-triphosphate - 5IMP Inosine 5-monophosphate - IDP Inosine 5-diphosphate - ITP Inosine 5-triphosphate - 5XMP Xanthosine 5-monophosphate - 5CMP Cytidine 5-monophosphate - dCMP 2 deoxycytidine 5-monophosphate - CTP Cytidine 5-triphosphate - 5UMP Uridine 5-monophosphate - 5TMP Thymidine 5-monophosphate - RP Ribose 5 monophosphate 相似文献
Résumé La femelle de la mouche méditerranéenne des fruits, Ceratitis capitata, préfère les solutions de sucrose contenant des ribonucléotides aux simples solutions de sucrose. Lórdre de préférence pour les nucléotides est le suivant: 5GMP>GTP>5CMP>5IMP >dGMP>5UMP>5AMP>5XMP=ATP =2 & 3GMP=RP>3AMP.Le 2AMP, la guanosine, l'inosine, l'adénine et le 5TMP provoquent une stimulation significative. Les femelles montrent aprés stérilisation par irradiation une attirance réduite pour le 5GMP par comparaison avec les femelles non-irradiées.La configuration moléculaire optimale pour la phagostimulation comprend: la phosphorylation en position 5 du ribose; des groupes hydroxyles libres en 2 et 3 sur le ribose; et un groupe NH2 en position 2 sur le noyau aromatique.Nous proposons que le 5GMP dans l'hydrolysat de levure puisse être utilisé pour mesurer la capacité de l'hydrolysat comme appât.
Abbreviations 5AMP Adenosine 5-monophosphate - 3AMP Adenosine 3-monophosphate - 2AMP Adenosine 2-monophosphate - dAMP 2-deoxyadenosine 5-monophosphate - ADP Adenosine 5-diphosphate - ATP Adenosine 5-triphosphate - 5GMP Guanosine 5-monophosphate - 2GMP Guanosine 2-monophosphate - 3GMP Guanosine 3-monophosphate - dGMP 2-deoxyguanosine 5-monophosphate - GDP Guanosine 5-diphosphate - GTP Guanosine 5-triphosphate - 5IMP Inosine 5-monophosphate - IDP Inosine 5-diphosphate - ITP Inosine 5-triphosphate - 5XMP Xanthosine 5-monophosphate - 5CMP Cytidine 5-monophosphate - dCMP 2 deoxycytidine 5-monophosphate - CTP Cytidine 5-triphosphate - 5UMP Uridine 5-monophosphate - 5TMP Thymidine 5-monophosphate - RP Ribose 5 monophosphate 相似文献
6.
Summary The incompatibility between F plasmids is transiently suppressed in Escherichia coli strain CSH54. As a result this strain is able to maintain two F factors or an F factor and a mini-F plasmid for considerably longer periods than normal strains. When selective pressure for two markers carried by two separate Fs (or an F and mini-F) is imposed on normal strains, the two plasmids tend to form a cointegrate structure which can be detected genetically by the joint transfer of both the markers upon mating. This does not happen in CSH54; instead, the two plasmids are maintained and transferred independently. Physical evidence for the maintenance of an F and a mini-F plasmid is provided by agarose gel electrophoresis. 相似文献
7.
The white rot basidiomycete Phanerochaete chrysosporium metabolized 4-ethoxy-3-methoxyphenyl-glycerol--guaiacyl ether (V) in low nitrogen, stationary cultures under which conditions the ligninolytic enzyme system is expressed. 4-Ethoxy-3-methoxyphenylglycerol XIII, guaicol and 4-ethoxy-3-methoxybenzyl alcohol (II) were isolated as metabolic products. Exogenously added XIII was rapidly converted to 4-ethoxy-3-methoxybenzyl alcohol indicating that it is an intermediate in the metabolism of V. P. chrysosporium also metabolized 1-(4-ethoxy-3-methoxyphenyl)-2-(2-methoxyphenoxy)-3-hydroxypropane VI. The degradation pathway for this dimer also included initial -ether cleavage and -hydroxylation of the diol product 1-(4-ethoxy-3-methoxyphenyl) 2,3 dihydroxypropane (XI) to yield the triol XIII which was cleaved at the , bond to yield 4-ethoxy-3-methoxybenzyl alcohol. Finally P. chrysosporium also cleaved the dimer 1-(4-ethoxy-3-methoxyphenyl)-2-(2-methoxyphenoxy)-1-hydroxypropane (VIII) at the -ether linkage yielding 1-(4-ethoxy-3-methoxyphenyl) 1,2 dihydroxypropane (IX) which was subsequently cleaved at the , bond to yield II. All of the results indicate that oxidative -ether cleavage is an important initial reaction in the metabolism of -aryl ether lignin substructure dimeric compounds. Metabolities were identified after comparison with chemically synthesized standards by gas liquid chromatography-mass spectrometry.Abbreviations GLC
Gas liquid chromatography
- TMSi
trimethylsilyl
- TLC
thin layer chromatography 相似文献
8.
Johannssen Walther Schütte Horst Mayer Hubert Mayer Frank 《Archives of microbiology》1984,140(2-3):265-270
Electron microscopy of negatively stained isolated restriction enzyme EcoRI revealed particle projections with triangular or square outlines, indicating that the enzyme, in its tetrameric state, is tetrahedron-like. The two dimers making up the tetramer appear to be arranged in two planes orthogonal to each other. Complexes formed by EcoRI with the plasmids pBR322 or pGW10 were investigated by electron microscopic spreading techniques. In the presence of Mg2+, EcoRI was bound to the DNA molecules to form pearl necklace-like aggregates. The number of bound EcoRI particles was much higher as the sum of EcoRI-and 5..AATT..3 sites (with exceptions, the 5..AATT..3 sites may function as one type of EcoRI* sites) along the DNAs, indicating unspecific binding. In the absence of Mg2+, EcoRI was bound to the DNA only at the recognition site for EcoRI and the sites where the tetranucleotide sequence 5..AATT..3 was present. A direct correlation of the local concentrations of the bases A and T within the flanking sequences of the binding sites with the frequency of EcoRI to the DNA was observed. Dimers and tetramers of the enzyme was found to bind to the DNA. Tetramers occasionally exhibited two binding sites for DNA as indicated by the observation of DNA loops originating at the sites of bound tetrameric EcoRI particles.Abbreviations BAC
Benzyldimethylalkylammoniumchloride
- bp
base pairs
- Kb
kilobases
- SDS
sodium dodecylsulfate
Enzymes (EC 3.1.23.13)
Restrictionendonuclease EcoRI
- (EC 3.1.23.21)
Restrictionendonuclease HindIII
- (EC 3.1.23.37)
Restrictionendonuclease SalGI
Dedicated Professor H. G. Schlegel on occasion of this 60th birthday 相似文献
9.
Structural differences in full-length cDNAs for two classes of sporamin,the major soluble protein of sweet potato tuberous roots 总被引:4,自引:0,他引:4
Summary Sporamin, which accounts for 80% of the total soluble proteins in sweet potato tuberous roots, consists of two polypeptide classes, A and B. The sporamin cDNA clones can also be classified into sporamin A and B subfamilies based on their sequence homologies, with intra-subfamily homologies being much higher than inter-subfamily homologies. The sequence of an essentially full-length cDNA for sporamin B was compared with that for sporamin A. The coding sequences of two cDNAs share 83% sequence homology. The sequences in the 5- and 3-noncoding regions show many deletions in addition to base substitutions. The endpoints of deletions longer than 4 bp match precisely to the endpoints of short direct repeats present in the other sequence, which suggests that these deletions are generated by slipped mispairing during DNA replication. In the 5- and 3-noncoding region of sporamin B cDNA, there are 5 bp direct repeats with sequences complementary to each other. Since most of these repeats are absent in sporamin A cDNA, these structural features may cause a difference in the secondary structure between A and B mRNAs and affect the translational efficiencies or stabilities of the mRNAs. Precursors for both classes of sporamin carry N-terminal extra-sequences which can be separated into a putative signal peptide segment and a segment enriched with basic amino acids. A two-step processing mechanism for the maturation of sporamin is suggested. 相似文献
10.
Maria Mulisch 《Protoplasma》1988,143(2-3):170-175
Summary Different fixation techniques were employed to obtain satisfactory fixation of the endoplasm ofStentor coeruleus for ultrastructural investigations. The nuclei ofS. coeruleus are surrounded by a flattened fenestrated cisterna. The space between the nuclear envelope and the cisterna (= perinuclear space) is continuous with the cytoplasm via channels. The envelopes of both, micronucleus and macronucleus, are connected to the fenestrated cisterna by filamentous material. This organization accounts for the close association between micronucleus and macronucleus inStentor coeruleus. The fenestrated cisterna is compared to similar structures occurring in other organisms, and its possible function is discussed.Abbreviations fC
fenestrated cisterna
- FV
food vacuole
- km
km fibers
- MaNu
macronucleus
- MiNu
micronucleus
- My
myonome
- NE
nuclear envelope
- PC
perinuclear cisterna
- PfC
pore of fenestrated cisterna
- PS
perinuclear cytoplasmic space
- EGTA
ethyleneglycol-bis-(-aminoethylether)-N,N,N,N-tetraacetic acid)
- GA
glutaraldehyde
- HEPES
N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid
- PEG
polyethylene glycol
- PIPES
piperazine-N,N-bis[2-ethanesulfonic acid]
- PTA
phosphotungstic acid 相似文献
11.
Specific DNA-labelling by exogenous thymidine-5''-monophosphate in Saccharomyces cerevisiae 总被引:2,自引:0,他引:2
Summary Strain 211-1aM of Saccharomyces cerevisiae was found to specifically incorporate into its nuclear and mitochondrial DNA exogenous 5-dTMP when it is incubated in a synthetic medium N rich in inorganic phosphate. 3-digestions of DNA from cells labelled with 32P-5-dTMP revealed that the 5-dTMP molecules pass through cell walls and membranes to the sites of DNA synthesis without being broken down. It is possible in medium N to generate DNA which almost totally derives its thymine-contents from external sources when rather high concentrations of 5-dTMP (approx. 100 g/ml) are offered. 相似文献
12.
Jeffrey Leung Hiroo Fukuda David Wing Jeff Schell Robert Masterson 《Molecular & general genetics : MGG》1991,230(3):463-474
Summary The dual MAS1-2 promoter regulating two divergently transcribed mannopine synthase genes has been widely employed in plant expression vectors. As part of an effort towards its rational design as a genetic engineering tool, we have undertaken a functional analysis of the promoter by deletion mutagenesis and by the use of hybrid promoter constructs. Our results indicate that the central region of the intergenic promoter is composed of at least four domains. Three of these contain complementary sequences, which can potentially hybridize to form alternative palindromic structures. These three domains can function cooperatively, and in an orientation-independent manner, in imparting a sevenfold higher expression level at the 2 end relative to the corresponding 1. The remaining domain is characterized by tracts of repeated A/T-rich elements, and appears to confer the weak activity at the MAS1 promoter end. However, even though this A/T-rich DNA segment is functional, our deletion analysis provided strong evidence that it is completely dispensable for wild-type promoter activity. In addition, the relative distances between these enhancer domains and the 1–2 TATA-proximal regions can have a pronounced influence on the level of expression in both directions. In young tobacco seedlings, the two promoter ends are expressed in similar, if not identical, tissues in the aerial parts of the plants, but major differences can be observed in roots. Transient expression assays using hybrid promoter constructs showed that cis-elements that can respond to auxin induction signals are redundant in nature, in that they are dispersed throughout the promoter and showed no obvious consensus sequence. 相似文献
13.
Isolation and characterization of a linear DNA plasmid from Streptomyces clavuligerus 总被引:3,自引:0,他引:3
Cheryl L. Keen Simona Mendelovitz Gerald Cohen Yair Aharonowitz Kenneth L. Roy 《Molecular & general genetics : MGG》1988,212(1):172-176
Summary A linear DNA plasmid (pSCL) has been isolated from Streptomyces clavuligerus by a method employing high concentrations of protease. Rate-zonal sedimentation on sucrose gradients was used to purify the plasmid. The plasmid is 12 kb in length and appears to be linked to protein at its 5 termini. A restriction endonuclease map of the plasmid for ten enzymes has been determined. Evidence for terminally repeated sequences is provided by cross-hybridization analysis. 相似文献
14.
Summary The active sites of actin of oneCharaceae species were found to interact with the endoplasmic factor from a different species. Protoplasm was suqueezed out of cells ofChara australis with vacuoles that had been perfused beforehand with a medium containing EGTA and Mg · ATP. Centrifugation of this protoplasmic mixture divided it into the supernatant composed of endoplasmic granules and the precipitate composed of chloroplasts and nuclei. When the endoplasmic granular aggregates were introduced into a tonoplast-freeNitella axilliformis cell treated with NEM to inactivate the endoplasmic factor, they became attached to theNitella gel and streamed longitudinally with the polarity. Treatment of the endoplasmic granules with the strong Mg2+chelator CyDTA (1,2-cyclohexane diamineN, N-tetraacetic acid) irreversibly inhibited reconstitution of the cytoplasmic streaming.Abbreviations APW
artificial pond water
- ATP
adenosine-5-triphosphoric acid
- CyDTA
cyclohexanediamine-N,N-tetraacetic acid
- DTT
dithiothreitol
- EGTA
ethyleneglycol-bis-(-aminoethylether)-N,N-tetraacetic acid
- HMM
heavy meromyosin
- NEM
N-ethylmaleimide
- PEP
phosphoenolypyruvate
- PIPES
piperazine-N,N-bis-(2-ethane-sulfonic acid)
- PK
pyruvate kinase
- PMSF
phenylmethylsulfonylfluoride 相似文献
15.
Toyoaki Tenzen Yohko Matsuda Hisako Ohtsubo Eiichi Ohtsubo 《Molecular & general genetics : MGG》1994,245(4):441-448
Tnr1 is a repetitive sequence in rice with several features characteristic of a transposable DNA element. Its copy number was estimated to be about 3500 per haploid genome by slot-blot hybridization. We have isolated six members of Tnr1 located at different loci by PCR (polymerase chain reaction) and determined their nucleotide sequences. The Tnr1 elements were similar in size and highly homologous (about 85%) to the Tnr1 sequence identified first in the Waxy gene in Oryza glaberrima. A consensus sequence of 235 by could be derived from the nucleotide sequences of all the Tnr1 members. The consensus sequence showed that base substitutions occurred frequently in Tnr1 by transition, and that Tnr1 has terminal inverted repeat sequences of 75 bp. Almost all the chromosomal sequences that flank the Tnr1 members were 5-PuTA-3 and 5-TAPy-3, indicating that Tnr1 transposed to 5-PuTAPy-3 sites, duplicating the TA sequence. PCR-amplified fragments from some rice species did not contain the Tnr1 members at corresponding loci. Comparison of nucleotide sequences of the fragments with or without a Tnr1 member confirmed preferential transposition of Tnr1 to 5-PuTAPy-3 sites, duplicating the TA sequence. One amplified sequence suggested that imprecise excision had occurred to remove a DNA segment containing a Tnr1 member and its neighboring sequences at the Waxy locus of rice species with genome types other than AA. We also present data that may suggest that Tnr1 is a defective form of an autonomous transposable element. 相似文献
16.
R. Lohrmann 《Journal of molecular evolution》1977,10(2):137-154
Summary Adenosine 5-phosphoramidates form when solutions containing adenosine 5-polyphosphates pnA (n 3) or P1, P2-diadenosine 5-diphosphate and amines are allowed to dry out. Mg ions catalyze these reactions. We have studied systems containing ammonia, imidazole, glycine, ethylenediamine and histamine. The yields of adenosine 5-phosphoramidates range from 10–50 % based on the nucleotide. The prebiotic significance of the reactions is discussed.Abbreviations Im
imidazole
- hist
histamine
- gly
glycine
- en
ethylenediamine
- CDI
1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride
- EDTA
ethylenediaminetetraacetic acid
- A
adenosine
- Pn (n = 1, 2 )
linear polyphosphate containing n phosphate residues
- pnA
adenosine 5-polyphosphate containing n phosphate residues
- ADP
adenosine 5-diphosphate
- ATP
adenosine 5-triphosphate
- AppA
P1, P2-diadenosine 5-diphosphate
- gly-pA
adenylyl-(5N)-glycine
- ImpA
adenosine 5-phosphorimidazolide
- NH2-pA
adenosine 5-phosphoramidate
- en-pA
adenylyl-(5N)-ethylenediamine
- hist (NH) - pA
adenosine 5-phospho-[2-(4-imidazolyl)-ethylamide]
- hist(Im)-pA
adenosine 5-phospho-[4-(2-aminoethyl)-imidazolide]
- enP1,2
phosphoramidates of ethylenediamine derived from H3PO4 and H4P2O7 相似文献
17.
A. H. G. P. Jayaratne D. L. Collins-Thompson J. T. Trevors 《Applied microbiology and biotechnology》1990,33(5):547-552
Summary 3-Aminoglycoside phosphotransferase [APH(3)] enzymes are a group responsible for resistance to the antibiotics kanamycin (Km) and neomycin (Nm) in bacteria. Escherichia coli ECT24, originally isolated from a meat sample, harboured an 83-kb conjugative R-plasmid (pRPJ24) that carries transferable resistance to Km and Nm. Plasmid pRPJ24 was transferred by conjugation to Enterobacter cloacae 94R, which was used as the source of plasmid DNA in development of a probe for the Km-resistance determinant. Random cloning of BamHI and HindIII double-digest restriction fragments of pRPJ24 in the pUC18 vector plasmid produced clones resistant to both Nm and Km carrying a 1.9-kb DNA insert. Southern hybridization of pRPJ24 cloned chimeric plasmid DNA (pKPJ94) showed homology with the APH(3)II gene from transposon Tn5. A PstI digest of pKPJ94 produced a 920-bp fragment which hybridized with the APH(3)II structural gene, and was used as a DNA probe for the APH(3)II subclass gene. A 980-bp BamHI fragment from plasmid pGH54 carrying the APH(3)I gene from transposon Tn903 was used as a subclass I probe. Total DNA from 206 randomly screened Km-resistant Enterobacteriaceae isolates from raw ground beef and chicken meat samples were examined for the occurrence of APH(3) subclass I and II using non-radioactively-labelled DNA probes. Thirty-six percent and 60% of the isolates examined carried subclass I and II resistances, respectively, in the isolates from chicken meat samples. The corresponding values for bacterial strains from raw ground beef samples were 51% and 72%, respectively. Four percent of the resistant bacterial isolates from chicken samples did not display homology to either probe. This value was 28% for bacterial isolates from ground beef. Three percent of bacterial isolates from chicken samples and 44% from ground beef samples displayed homology to both APH(3) I and II DNA probes.
Offprint requests to: A. H. G. P. Jayaratne 相似文献
18.
Gabriele Schultz Frank Ullrich Knut J. Heller Volkmar Braun 《Molecular & general genetics : MGG》1989,216(2-3):230-238
Summary The FhuA protein in the outer membrane of Escherichia coli serves as a multifunctional receptor for the phages T5, T1, 80, for colicin M, for ferrichrome (Fe3+-siderophore) and for the structurally related antibiotic, albomycin. To determine structural domains required for these receptor functions and for export, a fusion protein between FhuA and Iut (receptor for Fe3+-aerobactin and cloacin DF13) was constructed. In the FhuA-Iut hybrid protein, 24 amino acids of FhuA were replaced by 19 amino acids, 18 of which were from Iut. The number of plaque forming units of phage T5 and T1 on cells expressing FhuA-Iut was nearly as high as on cells expressing plasmid-encoded wild-type FhuA. However, 107-fold higher concentrations of phage 80 and 103 times more colicin M were required to obtain a zone of growth inhibition. Truncated FhuA proteins in which the last 24 amino acids at the carboxy-terminus were replaced by 16 (FhuA2) or 3 (FhuAT) amino acids could hardly be detected on polyacrylamide electrophoretograms of outer membrane proteins, due to proteolytic degradation. Sensitivity of cells expressing FhuA2 to phage T5 and T1 was reduced by several orders of magnitude and sensitivity to phage 80 and colicin M was totally abolished. In contrast, cells expressing FhuAT were nearly as sensitive to phage T5, T1, and 80 and to colicin M as cells containing FhuA-Iut. None of the constructs could grow on ferrichrome as sole iron source and none was sensitive to albomycin. Ferrichrome did not inhibit binding of T5 to TonB– cells expressing FhuA-Iut (as it did in FhuA+ cells) due to the lack of ferrichrome binding. It is concluded that very small deletions (relative to the size of FhuA with 714 amino acids) at the C-terminal end render FhuA susceptible to proteolytic cleavage. The C-terminal alterations affect sensitivity to FhuA-specific agents very differently. Apparently, the C-terminus is a very important part of FhuA regarding stability and activity. Expression of active FhuA and partially inactive FhuA derivatives in the same cell revealed no negative complementation, suggesting a FhuA monomer as functional unit. 相似文献
19.
The effect of an induced salmonid parr-to-smolt metamorphosis (smoltification) on the optical quality of the ocular lens was studied. In two separate experiments, rainbow trout (Oncorhynchus mykiss) parr were fed thyroxine in their diet to induce the metamorphosis. Lenses were excised at regular samplings during the treatment period and optically scanned using a custom scanning laser monitor. Radioimmunoassay was used to measure serum titers of thyroxine and 3,5,3-triiodo-L-thyronine. It was found that lens optical quality was consistently negatively correlated with 3,5,3-triiodo-L-thyronine levels, but not with thyroxine levels. To test if thyroid hormones are directly responsible for the change in optical quality, rainbow trout lenses were cultured for 72 h in a medium containing 3,5,3-triiodo-L-thyronine, but no effect was observed. The significance of these findings in the contexts of the fishes visual capabilities and smolting physiology is discussed. 相似文献
20.
S. Y. Zee 《Protoplasma》1992,170(1-2):86-89
Summary Cytoskeletons surrounding the chromosomes of the root tip cells ofPisum sativum and the generative cells ofAllamanda schottii were visualized using Triton X-100 extraction and scanning electron microscopy. The cytoskeleton surrounding the chromosome consisted of a reticulate network of fibres. This is the first report showing the existence of a chromosome exo-skeleton in plant cells.Abbreviations EGTA
ethyleneglycol-bis-(-aminoethylether) N,N,N,N-tetraacetic acid
- PIPES
piperazine-N,N-bis-(2-ethanesulfonic acid) 相似文献