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1.
Wenli Li Jianhua Ju Scott R. Rajski Hiroyuki Osada Ben Shen 《The Journal of biological chemistry》2008,283(42):28607-28617
Tautomycin (TTM) is a highly potent and specific protein phosphatase
inhibitor isolated from Streptomyces spiroverticillatus. The
biological activity of TTM makes it an important lead for drug discovery,
whereas its spiroketal-containing polyketide chain and rare dialkylmaleic
anhydride moiety draw attention to novel biosynthetic chemistries responsible
for its production. To elucidate the biosynthetic machinery associated with
these novel molecular features, the ttm biosynthetic gene cluster
from S. spiroverticillatus was isolated and characterized, and its
involvement in TTM biosynthesis was confirmed by gene inactivation and
complementation experiments. The ttm cluster was localized to a 86-kb
DNA region, consisting of 20 open reading frames that encode three modular
type I polyketide synthases (TtmHIJ), one type II thioesterase (TtmT), five
proteins for methoxymalonyl-S-acyl carrier protein biosynthesis
(Ttm-ABCDE), eight proteins for dialkylmaleic anhydride biosynthesis and
regulation (TtmKLMNOPRS), as well as two additional regulatory proteins (TtmF
and TtmQ) and one tailoring enzyme (TtmG). A model for TTM biosynthesis is
proposed based on functional assignments from sequence analysis, which agrees
well with previous feeding experiments, and has been further supported by
in vivo gene inactivation experiments. These findings set the stage
to fully investigate TTM biosynthesis and to biosynthetically engineer new TTM
analogs.Tautomycin (TTM)2
is a polyketide natural product first isolated in 1987 from Streptomyces
spiroverticillatus (1).
The structure and stereochemistry of TTM were established on the basis of
chemical degradation and spectroscopic evidence
(2-4).
TTM contains several features not common to polyketide natural products,
including a spiroketal group, a methoxymalonate-derived unit, and an acyl
chain bearing a dialkylmaleic anhydride moiety. Structurally related to TTM is
tautomycetin (TTN), which was first isolated in 1989 from Streptomyces
griseochromogenes following the discovery of TTM
(5,
6). The structure of TTN was
deduced by chemical degradation and spectroscopic analysis
(6), and its stereochemistry
was established by comparison of spectral data with those of TTN degradation
products and synthetic fragments
(7). Both TTM and TTN exist as
tautomeric mixtures composed of two interconverting anhydride and diacid forms
in approximately a 5:4 ratio under neutral conditions
(Fig. 1A)
(1,
2).Open in a separate windowFIGURE 1.A, structures of TTM and TTN in anhydride or diacid forms, and
biosynthetic origin of the dialkylmaleic anhydride by feeding experiments
using 13C-labeled acetate and propionate. The
methoxymalonate-derived unit in TTM is highlighted by the dotted oval.
R, polyketide moiety of TTM or TTN. B, selected natural product
inhibitors of PP-1 and PP-2A featuring a spiroketal or dialkylmaleric
anhydride moiety. C, selected natural products containing a
dialkylmaleic anhydride moiety.Early studies of TTM revealed its ability to induce morphological changes
in leukemia cells (8). However,
it was later realized that TTM is a potent and specific inhibitor of protein
phosphatases (PPs) PP-1 and PP-2A
(9). PP-1 and PP-2A are two of
the four major serine/threonine protein phosphatases that regulate diverse
cellular events such as cell division, gene expression, muscle contraction,
glycogen metabolism, and neuronal signaling in eukaryotic cells
(10-12).
Many natural product PP-1 and PP-2A inhibitors are known, including okadaic
acid (13), calyculin-A
(14), phoslactomycin,
spirastrellolide, and cantharidin
(15)
(Fig. 1B), as well as
TTM (16,
17), and TTN
(18). They have served as
useful tools to study PP-involved intracellular events in vivo and as
novel leads for drug discovery
(10-12).
Among these PP inhibitors, TTM and TTN are unique because of their PP-1
selectivity. Despite their structural similarities, TTM exhibits potent
specific inhibition of PP-1 and PP-2A with IC50 values of 22-32
nm and only a slight preference for PP-1
(18). Conversely, TTN shows
nearly a 40-fold higher binding affinity to PP-1 (IC50 = 1.6
nm) than to PP-2A (IC50 = 62 nm)
(18). Because the major
structural differences between TTM and TTN reside in the region distal to the
dialkylmaleic anhydride moiety (Fig.
1A), it has been proposed that differences in these
moieties might be responsible for the PP-1 selectivity
(17-19).
Finally, TTN also has an impressive immuno-suppressive activity
(20,
21), which is apparently
devoid for TTM. Clearly, the structural differences between these two
polyketides translate into large, exploitable differences in bio-activities,
yet an understanding of the biosynthetic origins of these differences remains
elusive.The spiroketal and dialkylmaleic anhydride features of TTM are uncommon for
polyketide natural products, as is the methoxymalonate-derived unit
(Fig. 1A). Few studies
have been carried out for spiroketal biosynthesis, yet it is reasonably common
among the phosphatase inhibitors such as calyculin A, okadaic acid, and a few
others (Fig. 1B). Less
common, but still found in the phosphatase inhibitor cantharidin, as well as
TTM and TTN, is the dialkylmaleic anhydride moiety
(Fig. 1B); this unit
appears in a number of other natural products
(Fig. 1C), although
the biosynthetic steps leading to this reactive moiety (a protected version of
a dicarboxylate) have not been rigorously investigated. Feeding experiments
with 13C-labeled precursors indicated that the anhydride of TTM and
TTN is assembled from a propionate and an as yet undefined C-5 unit
(Fig. 1A), which would
require novel chemistry for polyketide biosynthesis
(22). TTM differentiates
itself from all known PP-1 and PP-2A inhibitors by virtue of its unique
combination of both the dialkymaleic anhydride and spiroketal
functionalities.Multiple total syntheses of TTM and a small number of analogs have been
reported, confirming the predicted structure and absolute stereochemistry and
facilitating structure-activity relationship studies on PP inhibition and
apoptosis induction (19,
23-25).
These studies revealed that: (i) the C22-C26 carbon chain and the
dialkylmaleic anhydride are the minimum requirements for TTM bioactivity; (ii)
the C18-C21 carbon chain and 22-hydroxy group are important for PP inhibition;
(iii) the spiroketal moiety determines the affinity to specific protein
phosphatases; (iv) the active form is most likely the dicarboxylate; and (v)
3′-epi-TTM exhibits 1,000-fold less activity than TTM. However, taken as
a whole, none of the analogs had an improved potency or selectivity for PP-1
inhibition than the natural TTM
(19,
22-25).
As a result, a more specific inhibitor of PP-1 is urgently awaited to
differentiate the physiological roles of PP-1 and PP-2A in vivo and
to explore PPs as therapeutic targets for drug discovery.We have undertaken the cloning and characterization of the TTM biosynthetic
gene cluster from S. spiroverticillatus as the first step toward
engineering TTM biosynthesis for novel analogs
(26). We report here: (i)
cloning and sequencing of the complete ttm gene cluster, (ii)
determination of the ttm gene cluster boundaries, (iii)
bioinformatics analysis of the ttm cluster and a proposal for TTM
biosynthesis, and (iv) genetic characterization of the TTM pathway to support
the proposed pathway. Of particular interest has been the identification of
genes possibly related to dialkylmaleic anhydride biosynthesis, the unveiling
of the ttm polyketide synthase (PKS) genes predicted to select and
incorporate four different starter and extender units for TTM production, and
the apparent lack of candidate genes associated with spiroketal formation.
These findings now set the stage to engineer TTM analogs for novel PP-1- and
PP-2A-specific inhibitors by applying combinatorial biosynthetic methods to
the TTM biosynthetic machinery. 相似文献
2.
3.
Characterization of the Polyoxin Biosynthetic Gene Cluster from
Streptomyces cacaoi and Engineered Production of Polyoxin
H 总被引:1,自引:0,他引:1
Wenqing Chen Tingting Huang Xinyi He Qingqing Meng Delin You Linquan Bai Jialiang Li Mingxuan Wu Rui Li Zhoujie Xie Huchen Zhou Xiufen Zhou Huarong Tan Zixin Deng 《The Journal of biological chemistry》2009,284(16):10627-10638
4.
Cheng‐Zhen Gu Sheng‐Hao Yuan Jing Lü Yi‐Jun Qiao Yuan‐Yuan Song Mohammed Esmail AbdallaElzaki Chong‐Ren Yang Ying‐Jun Zhang Ren‐Sen Zeng 《化学与生物多样性》2019,16(1)
The actinomycete genus Streptomyces is characterized by producing bioactive secondary metabolites, including antibiotics. In this study, chemical and biological investigations were carried out on Streptomyces strain 4205 isolated from the paddy soil, leading to the identification and characterization of 10 albocycline‐type macrolides, among which 4 compounds were new, namely albocyclines A–D ( 1 – 4 ). The structures of 1 – 10 were identified according to the 1D‐ and 2D‐NMR spectroscopic data. Furthermore, compounds 1 – 10 were evaluated for antimicrobial activity. Compounds 5 – 7 displayed antimicrobial activities against Candidaalbicans ATCC 90028 with the same MIC value of 10.0 mg/mL and the IC50 values of 1.5, 1.0, and 1.0 mg/mL, respectively. Thus, the research on Streptomyces sp. is of vital significance for developing new antibiotic agents. 相似文献
5.
Zhi-Qiang Xiong Xiao-Rong Tu Sai-Jin Wei Lin Huang Xun-Hang Li Hui Lu Guo-Quan Tu 《PloS one》2013,8(8)
Antifungalmycin 702, a new polyene macrolide antibiotic produced by
Streptomyces
padanus
JAU4234, has a broad antifungal activity and may have potential future agricultural and/or clinical applications. However, the mechanism of antifungal action of antifungalmycin 702 remains unknown. Antifungalmycin 702 strongly inhibited mycelial growth and sclerotia formation/germination of Rhizoctonia solani. When treated with antifungalmycin 702, the hyphae morphology of
R
. solani
became more irregular. The membrane and the cellular organelles were disrupted and there were many vacuoles in the cellular space. The lesion in the plasma membrane was detected through the increase of membrane permeability, lipid peroxidation and leakage of cell constituents. In summary, antifungalmycin 702 may exert its antifungal activity against
R
. solani
by changing the structure of cell membranes and the cytoskeleton and interacting with the organelles. 相似文献
6.
7.
Background
Prion diseases are fatal neurodegenerative disorders characterized by misfolding and aggregation of the normal prion protein PrPC. Little is known about the details of the structural rearrangement of physiological PrPC into a still-elusive disease-associated conformation termed PrPSc. Increasing evidence suggests that the amino-terminal octapeptide sequences of PrP (huPrP, residues 59–89), though not essential, play a role in modulating prion replication and disease presentation.Methodology/Principal Findings
Here, we report that trypsin digestion of PrPSc from variant and sporadic human CJD results in a disease-specific trypsin-resistant PrPSc fragment including amino acids ∼49–231, thus preserving important epitopes such as the octapeptide domain for biochemical examination. Our immunodetection analyses reveal that several epitopes buried in this region of PrPSc are exposed in PrPC.Conclusions/Significance
We conclude that the octapeptide region undergoes a previously unrecognized conformational transition in the formation of PrPSc. This phenomenon may be relevant to the mechanism by which the amino terminus of PrPC participates in PrPSc conversion, and may also be exploited for diagnostic purposes. 相似文献8.
Purification, Characterization, and Antifungal Activity of Chitinase from Streptomyces venezuelae P10 总被引:1,自引:0,他引:1
Streptomyces venezuelae P10 could produce extracellular chitinase in a medium containing 0.6% colloidal chitin that was fermented for 96 hours at 30°C.
The enzyme was purified to apparent homogeneity with 80% saturation of ammonium sulfate as shown by chitin affinity chromatography
and DEAE-cellulose anion-exchange chromatography. Sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS-PAGE) of
the enzyme showed a molecular weight of 66 kDa. The chitinase was characterized, and antifungal activity was observed against
phytopathogens. Also, the first 15 N-terminal amino-acid residues of the chitinase were determined. The chitin hydrolysed
products were N-acetylglucosamine and N, N’-diacetylchitobiose. 相似文献
9.
A novel polyene compound NPP identified in a rare actinomycetes, Pseudonocardia autotrophica KCTC9441, was shown to contain an aglycone identical to nystatin but to harbor a unique di-sugar moiety, mycosaminyl-(α1-4)-N-acetyl-glucosamine, which led to higher solubility and reduced hemolytic activity. Although the nppDI was proved to be responsible for the transfer of first polyene sugar, mycosamine in NPP biosynthesis, the gene responsible for the second sugar extending glycosyltransferase (GT) as well as NPP post-PKS tailoring mechanism remained unknown. Here, we identified a NPP-specific second sugar extending GT gene named nppY, located at the edge of the NPP biosynthetic gene cluster. Targeted nppY gene deletion and its complementation proved that nppY is indeed responsible for the transfer of second sugar, N-acetyl-glucosamine in NPP biosynthesis. Site-directed mutagenesis on nppY also revealed several amino acid residues critical for NppY GT function. Moreover, a combination of deletions and complementations of two GT genes (nppDI and nppY) and one P450 hydroxylase gene (nppL) involved in the NPP post-PKS biosynthesis revealed that NPP aglycone is sequentially modified by the two different GTs encoded by nppDI and nppY, respectively, followed by the nppL-driven regio-specific hydroxylation at the NPP C10 position. These results set the stage for the biotechnological application of sugar diversification for the biosynthesis of novel polyene compounds in actinomycetes. 相似文献
10.
11.
Isolation and Characterization of a Histidine Biosynthetic Gene
in Arabidopsis Encoding a Polypeptide with Two Separate Domains for
Phosphoribosyl-ATP Pyrophosphohydrolase and Phosphoribosyl-AMP
Cyclohydrolase 下载免费PDF全文
Phosphoribosyl-ATP pyrophosphohydrolase (PRA-PH) and phosphoribosyl-AMP cyclohydrolase (PRA-CH) are encoded by HIS4 in yeast and by hisIE in bacteria and catalyze the second and the third step, respectively, in the histidine biosynthetic pathway. By complementing a hisI mutation of Escherichia coli with an Arabidopsis cDNA library, we isolated an Arabidopsis cDNA (At-IE) that possesses these two enzyme activities. The At-IE cDNA encodes a bifunctional protein of 281 amino acids with a calculated molecular mass of 31,666 D. Genomic DNA-blot analysis with the At-IE cDNA as a probe revealed a single-copy gene in Arabidopsis, and RNA-blot analysis showed that the At-IE gene was expressed ubiquitously throughout development. Sequence comparison suggested that the At-IE protein has an N-terminal extension of about 50 amino acids with the properties of a chloroplast transit peptide. We demonstrated through heterologous expression studies in E. coli that the functional domains for the PRA-CH (hisI) and PRA-PH (hisE) resided in the N-terminal and the C-terminal halves, respectively, of the At-IE protein. 相似文献
12.
13.
Ryan F. Seipke 《PloS one》2015,10(1)
Streptomyces spp. are robust producers of medicinally-, industrially- and agriculturally-important small molecules. Increased resistance to antibacterial agents and the lack of new antibiotics in the pipeline have led to a renaissance in natural product discovery. This endeavor has benefited from inexpensive high quality DNA sequencing technology, which has generated more than 140 genome sequences for taxonomic type strains and environmental Streptomyces spp. isolates. Many of the sequenced streptomycetes belong to the same species. For instance, Streptomyces albus has been isolated from diverse environmental niches and seven strains have been sequenced, consequently this species has been sequenced more than any other streptomycete, allowing valuable analyses of strain-level diversity in secondary metabolism. Bioinformatics analyses identified a total of 48 unique biosynthetic gene clusters harboured by Streptomyces albus strains. Eighteen of these gene clusters specify the core secondary metabolome of the species. Fourteen of the gene clusters are contained by one or more strain and are considered auxiliary, while 16 of the gene clusters encode the production of putative strain-specific secondary metabolites. Analysis of Streptomyces albus strains suggests that each strain of a Streptomyces species likely harbours at least one strain-specific biosynthetic gene cluster. Importantly, this implies that deep sequencing of a species will not exhaust gene cluster diversity and will continue to yield novelty. 相似文献
14.
Sara Teixeira de Macedo-Silva Julio A. Urbina Wanderley de Souza Juliany Cola Fernandes Rodrigues 《PloS one》2013,8(12)
Leishmaniasis, caused by protozoan parasites of the Leishmania genus, is one of the most prevalent neglected tropical diseases. It is endemic in 98 countries, causing considerable morbidity and mortality. Pentavalent antimonials are the first line of treatment for leishmaniasis except in India. In resistant cases, miltefosine, amphotericin B and pentamidine are used. These treatments are unsatisfactory due to toxicity, limited efficacy, high cost and difficult administration. Thus, there is an urgent need to develop drugs that are efficacious, safe, and more accessible to patients. Trypanosomatids, including Leishmania spp. and Trypanosoma cruzi, have an essential requirement for ergosterol and other 24-alkyl sterols, which are absent in mammalian cells. Inhibition of ergosterol biosynthesis is increasingly recognized as a promising target for the development of new chemotherapeutic agents. The aim of this work was to investigate the antiproliferative, physiological and ultrastructural effects against Leishmania amazonensis of itraconazole (ITZ) and posaconazole (POSA), two azole antifungal agents that inhibit sterol C14α-demethylase (CYP51). Antiproliferative studies demonstrated potent activity of POSA and ITZ: for promastigotes, the IC50 values were 2.74 µM and 0.44 µM for POSA and ITZ, respectively, and for intracellular amastigotes, the corresponding values were 1.63 µM and 0.08 µM, for both stages after 72 h of treatment. Physiological studies revealed that both inhibitors induced a collapse of the mitochondrial membrane potential (ΔΨm), which was consistent with ultrastructural alterations in the mitochondrion. Intense mitochondrial swelling, disorganization and rupture of mitochondrial membranes were observed by transmission electron microscopy. In addition, accumulation of lipid bodies, appearance of autophagosome-like structures and alterations in the kinetoplast were also observed. In conclusion, our results indicate that ITZ and POSA are potent inhibitors of L. amazonensis and suggest that these drugs could represent novel therapies for the treatment of leishmaniasis, either alone or in combination with other agents. 相似文献
15.
A strain of Streptomyces sp. (M10) antagonistic to Botrytis cinerea was isolated from orchard soil obtained from Jeju Island, Korea. An antifungal substance (CN1) was purified from the culture extracts of the strain, and then identified as valinomycin through extensive spectroscopic analyses. Valinomycin showed potent in vitro antifungal activity against Botrytis cinerea and also in vivo control efficacy against Botrytis blight development in cucumber plants. Overall, the disease control efficacy of valinomycin was similar to that of vinclozolin, a commercial fungicide. This study provides the first report on the disease control efficacy of valinomycin against Botrytis blight. 相似文献
16.
Ron A. Salzman Irina Tikhonova Bruce P. Bordelon Paul M. Hasegawa Ray A. Bressan 《Plant physiology》1998,117(2):465-472
During ripening of grape
(Vitis labruscana L. cv Concord) berries, abundance of
several proteins increased, coordinately with hexoses, to the extent
that these became the predominant proteins in the ovary. These proteins
have been identified by N-terminal amino acid-sequence analysis and/or
function to be a thaumatin-like protein (grape osmotin), a
lipid-transfer protein, and a basic and an acidic chitinase. The basic
chitinase and grape osmotin exhibited activities against the principal
grape fungal pathogens Guignardia bidwellii and
Botrytis cinerea based on in vitro growth assays. The
growth-inhibiting activity of the antifungal proteins was substantial
at levels comparable to those that accumulate in the ripening fruit,
and these activities were enhanced by as much as 70% in the presence
of 1 m glucose, a physiological hexose concentration in
berries. The simultaneous accumulation of the antifungal proteins and
sugars during berry ripening was correlated with the characteristic
development of pathogen resistance that occurs in fruits during
ripening. Taken together, accumulation of these proteins, in
combination with sugars, appears to constitute a novel, developmentally
regulated defense mechanism against phytopathogens in the maturing
fruit.Plants have evolved a number of strategies to resist fungal
infection. One strategy involves the accumulation of defense proteins
that have direct inhibitory activity against the hyphae and/or
germinating spores of the pathogen. Among these are PR proteins
including chitinases (PR-3 family), thaumatin-like proteins (PR-5
family), and nsLTPs. Typically, these antifungal proteins are expressed
constitutively at low levels in cells and accumulate in response to
fungal attack or in response to other inducers of acquired resistance
(Uknes et al., 1992). Reproductive organs are apparently an exception
to induced acquired resistance. Presumably, the importance of flowers
and ovaries to the maintenance of the species has mandated that
reproductive organs acquire pathogen resistance during development.
Developmentally regulated expression of PR proteins has been observed
in floral organs (Lotan et al., 1989; Neal et al., 1990), including
numerous examples of defensive gene mRNA accumulation in fruits.
However, comparatively few data are available that interrelate
developmental accumulation of antifungal proteins and the acquisition
of resistance against fruit pathogens (Fils-Lycaon et al., 1996; Meyer
et al., 1996).Another physiological adaptation of plants that affects fungal
pathogenesis, but one that has received considerably less attention, is
the accumulation of sugars. Results from studies of several
host/pathogen systems have implicated accumulation or depletion of
sugars in resistance to fungal infection (VanderPlank, 1984). Increased
susceptibility to fungi in sugar-depleted vegetative tissues, a
phenomenon termed “sink-induced loss of resistance,” has been
documented in tomato (Horsfall, 1975), cotton (Eaton and Rigler, 1946),
and maize (Holbert et al., 1935). Conversely, moderate levels of sugars
can enhance colonization rates of some fungal pathogens, presumably
because these are important sources of C for the microbes (Mains,
1917). However, higher levels of sugars can reverse this effect,
leading to decreased susceptibility, a phenomenon termed “high-sugar
resistance” (Horsfall and Dimond, 1957). This reversal of
susceptibility has been suggested to occur as a result of high sugar
levels furnishing an osmotic challenge to the fungi and suppressing
their colonization of the plant (VanderPlank, 1984).We report here that accumulation of hexoses in grape (Vitis
labruscana L. cv Concord) berries is accompanied by a
developmental-stage-specific increase in a suite of proteins that are
homologous to proteins known to be antifungal determinants. These
proteins have been identified as a thaumatin-like protein (Salzman et
al., 1994) (here we have named it GO), chitinases (both CBC and AC
forms), and a nsLTP. Physiological levels of GO or CBC assayed in vitro
alone or in combination with physiological levels of Glc exhibited
individual and/or combinatorial activities against the important grape
pathogens Guignardia bidwellii, the causal agent of black
rot, and Botrytis cinerea. The interaction of the antifungal
proteins and hexoses appears to constitute a developmentally regulated
defense mechanism to restrict fungal pathogen infection as seeds are
maturing in ripening berries. 相似文献
17.
Rafael Silva-Rocha Marjorie Cornejo Pontelli Gilvan Pessoa Furtado Livia Soares Zaramela Tie Koide 《PloS one》2015,10(6)
Our ability to genetically manipulate living organisms is usually constrained by the efficiency of the genetic tools available for the system of interest. In this report, we present the design, construction and characterization of a set of four new modular vectors, the pHsal series, for engineering Halobacterium salinarum, a model halophilic archaeon widely used in systems biology studies. The pHsal shuttle vectors are organized in four modules: (i) the E. coli’s specific part, containing a ColE1 origin of replication and an ampicillin resistance marker, (ii) the resistance marker and (iii) the replication origin, which are specific to H. salinarum and (iv) the cargo, which will carry a sequence of interest cloned in a multiple cloning site, flanked by universal M13 primers. Each module was constructed using only minimal functional elements that were sequence edited to eliminate redundant restriction sites useful for cloning. This optimization process allowed the construction of vectors with reduced sizes compared to currently available platforms and expanded multiple cloning sites. Additionally, the strong constitutive promoter of the fer2 gene was sequence optimized and incorporated into the platform to allow high-level expression of heterologous genes in H. salinarum. The system also includes a new minimal suicide vector for the generation of knockouts and/or the incorporation of chromosomal tags, as well as a vector for promoter probing using a GFP gene as reporter. This new set of optimized vectors should strongly facilitate the engineering of H. salinarum and similar strategies could be implemented for other archaea. 相似文献
18.
Greenhouse and field experiments were conducted to determine the effects of phenamiphos and/or alachlor on early growth of soybean, root morphology, and infection and resurgence of Heterodera glycines (race 1). All tests were planted to ''Ransom'' soybeans. In greenhouse experiments without nematodes, root growth was inhibited at 5 days by alachlor treatments and at 10 days by phenamiphos treatments; with nematodes, phenamiphos treatments enhanced root growth. Phenamiphos also suppressed early penetration of soybean roots by H. glycines in the greenhouse. Early soybean growth parameters among treatments were generally similar in the field. Nematode penetration was limited with treatments containing phenamiphos at one location. Plants treated with only alachlor had less nematode infection than did the control; however, plants treated with herbicide/nematicide combinations had more nematode penetration than did plants treated with phenamiphos alone. Alterations of root growth and interference with the efficacy of phenamiphos are two processes by which alachlor may enhance soybean susceptibility or suitability to H. glycines. 相似文献
19.
Deletions Generated by the Transposon Tn10 in the srl recA Region of the ESCHERICHIA COLI K-12 Chromosome 总被引:45,自引:0,他引:45 下载免费PDF全文
A negative regulatory gene for the srl operon (srlR) was recognized by the characteristics of an insertion mutation generated by the transposon Tn10 determining tetracycline resistance. This finding is discussed in light of previous hypotheses on the regulation of the srl genes, which mediate metabolism of glucitol (i.e., sorbitol). Mapping showed that the order of genes in this region is: srlR srlD srlC recA alaS. Using two different methods, five mutations of both srl and recA were detected. The phenotype conferred by these mutations, UV sensitivity and extreme recombination deficiency, is characteristic of standard recA point mutants. Three of the mutations were deletions that also removed the genes for tetracycline resistance of the nearby transposon. A fourth mutation ended at a distance from Tn10 sufficient to allow separation of the two by recombination following P1 transduction; our tests did not allow us to conclude whether this mutation was an inversion or a deletion. The fifth mutation was a deletion that seemed to end immediately adjacent to the boundary of Tn10, proximal to recA. Mechanisms for the generation of these srl recA mutations are discussed. 相似文献
20.
The paulomycins are a group of glycosylated compounds featuring a unique paulic
acid moiety. To locate their biosynthetic gene clusters, the genomes of two
paulomycin producers, Streptomyces paulus NRRL 8115 and
Streptomyces sp. YN86, were sequenced. The paulomycin
biosynthetic gene clusters were defined by comparative analyses of the two
genomes together with the genome of the third paulomycin producer
Streptomyces albus J1074. Subsequently, the identity of the
paulomycin biosynthetic gene cluster was confirmed by inactivation of two genes
involved in biosynthesis of the paulomycose branched chain
(pau11) and the ring A moiety (pau18) in
Streptomyces paulus NRRL 8115. After determining the gene
cluster boundaries, a convergent biosynthetic model was proposed for paulomycin
based on the deduced functions of the pau genes. Finally, a
paulomycin high-producing strain was constructed by expressing an
activator-encoding gene (pau13) in S.
paulus, setting the stage for future investigations. 相似文献