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The fit locus, encoding two proteins, FitA and FitB, was identified in a genetic screen for Neisseria gonorrhoeae determinants that affect trafficking across polarized epithelial cells. To better understand how the locus may control these activities, we have undertaken a biochemical analysis of FitA and FitB. FitA is a DNA-binding protein with a putative ribbon-helix-helix (RHH) motif. Purified FitA forms a homodimer that binds a 150 bp fit promoter sequence containing the translational start site. A putative beta strand mutant of FitA, FitA(R7A), is unable to bind this DNA, supporting further that FitA is a RHH protein. FitB interacts with FitA to form a 98 kDa complex. FitA/B binds DNA with a 38-fold higher affinity than the FitA homodimer. In DNase I footprint assays, FitA/B protects a 62-bp region within the fit promoter containing the predicted -10 sequence and an 8-bp inverted repeat, TGCTATCA-N(12)-TGATAGCA. FitA/B(His) is able to bind to either half-site alone with high affinity. 相似文献
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Neisseria gonorrhoeae is a sexually transmitted pathogen that initiates infections in humans by adhering to the mucosal epithelium of the urogenital tract. The bacterium then enters the apical region of the cell and traffics across the cell to exit into the subepithelial matrix. Mutations in the fast intracellular trafficking (fitAB) locus cause the bacteria to transit a polarized epithelial monolayer more quickly than the wild-type parent and to replicate within cells at an accelerated rate. Here, we describe the crystal structure of the toxin-antitoxin heterodimer, FitAB, bound to a high affinity 36-bp DNA fragment from the fitAB promoter. FitA, the antitoxin, binds DNA through its ribbon-helix-helix motif and is tethered to FitB, the toxin, to form a heterodimer by the insertion of a four turn alpha-helix into an extensive FitB hydrophobic pocket. FitB is composed of a PIN (PilT N terminus) domain, with a central, twisted, 5-stranded parallel beta-sheet that is open on one side and flanked by five alpha-helices. FitB in the context of the FitAB complex does not display nuclease activity against tested PIN substrates. The FitAB complex points to the mechanism by which antitoxins with RHH motifs can block the activity of toxins with PIN domains. Interactions between two FitB molecules result in the formation of a tetramer of FitAB heterodimers, which binds to the 36-bp DNA fragment and provides an explanation for how FitB enhances the DNA binding affinity of FitA. 相似文献
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Physiological parameters such as viability, gross RNA synthesis,β-galactosidase induction, development of phages T4, T7 andλ have been studied in temperature-sensitiveEscherichia coli strains harbouring fit A76,fit A24 andfit A76fit A24 mutations in rpoB+ andrpoB240 genetic backgrounds. The efficiently of expression of these functions is influenced by thefit A alleles depending upon the medium of growth and/or temperature. Strains harbouring therpoB240 mutation and thefit A76 mutation, either alone or together with thefit A24 mutation, are rifampicin-sensitive even at the perfssive temperature. The results suggest possible interaction between
thefit A gene product and RNA polymerase invivo.
This paper is dedicated to Proof. S. Krishnaswamy on his Sixty First Birthday. 相似文献
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《Experimental mycology》1984,8(3):261-265
Green-spore revertants of a dominant-yellow conidial-color mutant (yB35) ofAspergillus nidulans were found to be abnormal in sexual development. Sexual fruiting bodies (cleistothecia) either were completely absent or were overproduced. For each of three revertants analyzed, reversion was due to a second-site suppressor mutation unlinked to theyB locus. Outcrossed strains that carried the suppressor mutations free of theyB mutation retained the aberrations in sexual development exhibited by the corresponding revertants. This finding provides a powerful screening method for rare sexual cycle mutants, since theyB revertants are manifested as easily identified green patches on a lawn of yellow conidia. Possible mechanisms of suppression of theyB phenotype are discussed. 相似文献
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Reversion of a streptomycin-dependent strain of Escherichia coli 总被引:13,自引:0,他引:13
Summary A streptomycin dependent, spectinomycin resistant mutant ofEscherichia coli was used to select spontaneous phenotypic revertants to non-dependence on streptomycin. The ribosomes from one such revertant, which is inhibited by both streptomycin and spectinomycin, were analyzedin vitro. The altered protein responsible for the suppression of the streptomycin dependent phenotype was identified; this protein is 30S-10. The genetic locus for this mutation is a newly identified locus and it has been positioned close to thestr locus. The identification of the altered component responsible for the suppression of the spectinomycin resistant phenotype may be the same as that for the streptomycin dependent phenotype, but this is unproven. 相似文献
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Summary Twenty-one suppressor gene mutations which suppress the met-5.1 missense mutation of Coprinus were separated into six groups (A-F) on the basis of dominance or recessiveness, linkage to the met-5 locus, comlementation in heterozygous cells and growth behaviour. The actual number of suppressor loci could not be determined because crosses between suppressed mutants were inviable. The allele specificity of group A, C, D and F suppressors was confirmed by appropriate crosses. Group B and E suppressors were not tested because of close linkage to the met-5 locus. No evidence for functional suppression of met-5 mutations was obtained thus it is likely that all the suppressors cause translational corelation of met-5.1. Suppressors in four groups (C-F) have properties expected of tRNA structural gene mutations: the group C mutation is dominant, the other mutations are recessive but do not complement in heterozygous cells. The relative efficiencies of the tRNA species involved was assessed by comparing the degree to which the different sup
+ mutations depressed the growth rate on methionine supplemented medium. The dominant mutation depressed growth to the greatest extent and is, therefore, the most efficient suppressor. The least efficient suppressors did not depress growth at all. When growth was compared on minimal medium it was found that the more efficient the suppressor the less well it restored growth. The mutations in groups A and B depressed growth more than the tRNA mutations but affect some other component in translation because they are recessive and complement normally. It is suggested that they may act to alter tRNA modifying enzymes. 相似文献
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A convenient assay to score repeat-induced point mutation (RIP) inNeurospora employs theerg-3 locus as a mutagenesis target. Using this assay we screened 132 wild-isolatedNeurospora crassa strains for ability to dominantly suppress RIP. RIP was exceptionally inefficient in crosses with the wild isolates Sugartown
(P0854) and Adiopodoume-7 (P4305), thereby suggesting the presence of dominant RIP suppressors in these strains. In other
experiments, we found no evidence for dominant RIP suppression by theSpore killer haplotypesSk-2 andSk-3. 相似文献
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Anne Debost-Legrand Guillaume Legrand Gaelle Moulillot Christine Francannet Bertrand Bocly Ioannis Theodoroub Catherine Paillard 《Gene》2013
X-linked agammaglobulinemia (XLA) or Bruton disease is a relatively rare constitutionally immune disorder due to a genetic mutation of BTK (Bruton tyrosine kinase) gene which encodes for BTK protein. BTK is a signal-transducing protein expressed in hematopoietic lineages. The genetic disorder is responsible for B cell lymphocytes' maturation arrest. The humoral immunodeficiency caused by BTK mutation is linked with recurrent bacterial and viral infections. Genetic investigations of the prepositus as well as the other members of the family are necessary to characterize a mutation in BTK gene to confirm the diagnosis and reveal a hereditary transmission or de novo mutation. 相似文献
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The known locus of fructose-6-phosphate kinase mutations (pfkA) in Escherichia coli is at 76 min on the genetic map. We have now found another gene, pfkB, at 33 min, mutation of which suppresses pfkA mutations. The suppression is not informational, and pfkB may be a second gene for fructose-6-phosphate kinase activity. 相似文献
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A recessive lethal mutation ofDrosophila melanogaster which as heterozygote enhances the phenotype of several mutant combinations of thebithorax-complex (BX-C) is described here; it is calledEnhancer of bithorax (E(bx)2). The linkage group and the map position of this mutation have been determined; it maps on the third chromosome at - 1.65 map units. It has been cytologically localised to the region 61A1-6. This locus is a possible candidate for positive control of BX-C. 相似文献
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Thirteen cadmium-resistant mutants ofAspergillus nidulans have been isolated which can grow on higher levels of cadmium than can wild-type strains. In each case, resistance results from a single gene mutation: these identify two new loci. Three mutants are located in thecadA gene on chromosome IV; the other ten have been mapped to thecadB locus, which is tightly linked to themethB gene on chromosome VI. 相似文献
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Further studies on theisfA mutation responsible for anti-SOS and antimutagenic activities inEscherichia coli are described. We have previously shown that theisfA mutation inhibits mutagenesis and other SOS-dependent phenomena, possibly by interfering with RecA coprotease activity. TheisfA mutation has now been demonstrated also to suppress mutator activity inE. coli recA730 andrecA730 lexA51(Def) strains that constitutively express RecA coprotease activity. We further show that the antimutator activity of theisfA mutation is related to inhibition of RecA coprotease-dependent processing of UmuD. Expression of UmuD' from plasmid pGW2122 efficiently restores UV-induced mutagenesis in therecA730 isfA strain and partially restores its mutator activity. On the other hand, overproduction of UmuD'C proteins from pGW2123 plasmid markedly enhances UV sensitivity with no restoration of mutability. 相似文献
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Summary The leaky expression of the yeast mitochondrial geneoxi1, containing a frameshift mutation (+1), is caused by natural frameshift suppression, as shown previously (Fox and Weiss-Brummer
1980). A drastic decrease in the natural level of frameshifting is found in the presence of thepar
r-454 mutation, localized at the 3′ end of the 15 S rRNA gene. This mutation causes resistance to the antibiotic paronomycin
in the yeast strains D273-10B and KL14-4A (Li et al. 1982; Tabak et al. 1982). The results of this study imply that in the
yeast strain 777-3A this mutation alone is sufficient for restriction of the level of natural frameshifting but is insufficient
to confer resistance to paromomycin. A second mutation, arising spontaneously with a frequency of 10−4 leads, in combination with thepar
r-454 mutation, to full paromomycin resistance in strain 777-3A. 相似文献
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James J. Giovannoni Erick N. Noensie Diane M. Ruezinsky Xianghuai Lu Samantha L. Tracy Martin W. Ganal Gregory B. Martin Klaus Pillen Kevin Albert Steven D. Tankslev 《Molecular genetics and genomics : MGG》1995,248(2):195-206
Ripening represents a complex developmental process unique to plants. We are using tomato fruit ripening mutants as tools to understand the regulatory components that control and coordinate the physiological and biochemical changes which collectively confer the ripe phenotype. We have genetically characterized two loci which result in significant inhibition of the ripening process in tomato,ripening-inhibitor (rin), andnon-ripening (nor), as a first step toward isolating genes likely to encode key regulators of this developmental process. A combination of pooled-sample mapping as well as classical restriction fragment length polymorphism (RFLP) analysis has permitted the construction of high-density genetic maps for the regions of chromosomes 5 and 10 spanning therin andnor loci, respectively. To assess the feasibility of initiating a chromosome walk, physical mapping of high molecular weight genomic DNA has been employed to estimate the relationship between physical distance (in kb) and genetic distance (in cM) around the targeted loci. Based on this analysis, the relationship in the region spanning therin locus is estimated to be 200–300 kb/cM, while thenor locus region ratio is approximately 200 kb/1 cM. Using RFLP markers tightly linked torin andnor, chromosome walks have been initiated to both loci in a yeast artificial chromosome (YAC) library of tomato genomic DNA. We have isolated and characterized several YAC clones linked to each of the targeted ripening loci and present genetic evidence that at least one YAC clone contains thenot locus. 相似文献
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T. V. Dolmatovich S. V. Malyshev S. P. Sosnikhina N. V. Tsvetkova N. A. Kartel A. V. Voylokov 《Russian Journal of Genetics》2013,49(5):511-516
The sy19 mutation, which impairs the homology of meiotic chromosome synapsis in rye, were mapped using a specially created F2 population by means of isozyme Acph1 locus and microsatellite (SSR) markers. The sy19 gene was localized in the chromosome 7R in the pericentromeric region of long arm based on the linked inheritance with the Acph1 locus. The locus was linked with five rye SSR markers, with the Xrems1234 locus being located closest to the sy19 gene (6.4 cM). The genetic map of the analyzed chromosome 7R region includes ten markers and the sy19 locus. A possible function of the Sy1 and Sy19 genes based on the data on comparative genomics is discussed. 相似文献