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Identification and Characterization of pvuA, a Gene Encoding the Ferric Vibrioferrin Receptor Protein in Vibrio parahaemolyticus. Tatsuya Funahashi, 2002.We previously reported that Vibrio parahaemolyticus expresses two outer membrane proteins of 78 and 83 kDa concomitant with production of siderophore vibrioferrin in response to iron starvation stress and that these proteins are the ferric vibrioferrin receptor and heme receptor, respectively (S . Yamamoto, T . Akiyama, N . Okujo, S . Matsuura, and S . Shinoda, Microbiol . Immunol . 39:759-766, 1995; S . Yamamoto, Y . Hara, K . Tomochika, and S . Shinoda, FEMS Microbiol . Lett . 128:195-200, 1995) . In this study, the Fur titration assay (FURTA) system was applied to isolate DNA fragments containing a potential Fur box from a genomic DNA library of V . parahaemolyticus WP1 . Sequencing a 3.2-kb DNA insert in one FURTA-positive clone revealed that an amino acid sequence deduced from a partial gene, which was preceded by a full-length gene (psuA) encoding a receptor for a siderophore of unknown origin, was consistent with the N-terminal amino acid sequence of the 78-kDa ferric vibrioferrin receptor . Then, the full-length gene (pvuA) encoding the ferric vibrioferrin receptor was cloned and characterized . The deduced protein encoded by pvuA displayed the highest similarity (31% identity; 48% similarity) to RumA, a ferric rhizoferrin receptor of Morganella morganii . Primer extension and Northern blot analyses indicated that psuA and pvuA constitute an operon which is transcribed from a Fur-repressed promoter upstream of psuA . The product of the pvuA gene and its function were confirmed by generating a pvuA-disrupted mutant, coupled with genetic complementation studies . A mutant with disruption in the upstream psuA gene also displayed a phenotype impaired in the utilization of ferric vibrioferrin . Definition of a Second Bacillus subtilis pur Regulon Comprising the pur and xpt-pbuX Operons plus pbuG, nupG (yxjA), and pbuE (ydhL). Lars Engholm Johansen, 2003.In Bacillus subtilis expression of genes or operons encoding enzymes and other proteins involved in purine synthesis is affected by purine bases and nucleosides in the growth medium . The genes belonging to the PurR regulon (purR, purA, glyA, guaC, pbuO, pbuG, and the pur, yqhZ-folD, and xpt-pbuX operons) are controlled by the PurR repressor, which inhibits transcription initiation . Other genes are regulated by a less-well-described transcription termination mechanism that responds to the presence of hypoxanthine and guanine . The pur operon and the xpt-pbuX operon, which were studied here, are regulated by both mechanisms . We isolated two mutants resistant to 2-fluoroadenine in which the pur operon and the xpt-pbuX operon are expressed at increased levels in a PurR-independent manner . The mutations were caused by deletions that disrupted a potential transcription terminator structure located immediately upstream of the ydhL gene . The 5' part of the ydhL leader region contained a 63-nucleotide (nt) sequence very similar to the 5' ends of the leaders of the pur and xpt-pbuX operons . Transcripts of these regions may form a common tandem stem-loop secondary structure . Two additional genes with potential leader regions containing the 63-nt sequence are pbuG, encoding a hypoxanthine-guanine transporter, and yxjA, which was shown to encode a purine nucleoside transporter and is renamed nupG . Transcriptional lacZ fusions and mutations in the 63-nt sequence encoding the possible secondary structures provided evidence that expression of the pur and xpt-pbuX operons and expression of the ydhL, nupG, and pbuG genes are regulated by a common mechanism . The new pur regulon is designated the XptR regulon . Except for ydhL, the operons and genes were negatively regulated by hypoxanthine and guanine . ydhL was positively regulated . The derived amino acid sequence encoded by ydhL (now called pbuE) is similar to the amino acid sequences of metabolite efflux pumps . When overexpressed, PbuE lowers the sensitivity to purine analogs . Indirect evidence indicated that PbuE decreases the size of the internal pool of hypoxanthine . This explains why the hypoxanthine- and guanine-regulated genes are expressed at elevated levels in a mutant that overexpresses pbuE . Corrected Sequence of the Bacteriophage P22 Genome. Marisa L. Pedulla, 2003.We report the first accurate genome sequence for bacteriophage P22, correcting a 0.14% error rate in previously determined sequences . DNA sequencing technology is now good enough that genomes of important model systems like P22 can be sequenced with essentially 100% accuracy with minimal investment of time and resources .
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