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Novel Non-mecA-Containing Staphylococcal Chromosomal Cassette Composite Island Containing pbp4 and tagF Genes in a Commensal Staphylococcal Species: a Possible Reservoir for Antibiotic Resistance Islands in Staphylococcus aureus. Kanokporn Mongkolrattanothai, 2004.Among methicillin-resistant Staphylococcus aureus isolates, a staphylococcal chromosomal cassette containing the mecA gene (SCCmec) is integrated into the chromosome at a unique site . SCCmec also contains unique ccrAB recombinase genes mediating its integration and excision from the genome and is flanked by characteristic left and right direct- and inverted-repeat sequences . A few non-mecA-containing SCC elements that have the other molecular features described above have recently been described . The origin of these cassettes is not clear . We have identified two new members of the SCC family integrated within orfX in Staphylococcus epidermidis strain ATCC 12228, neither of which carries mecA . One is a 57-kb element flanked by a unique 28-bp SCC direct repeat . It was called the SCC composite island (SCC-CI) because it carries a 19-kb SCC element (SCCpbp4) nested within it . SCCpbp4 contains pbp4 and tagF genes, as well as one pair of ccrAB genes (allotype 2) flanked by classical SCC-specific terminal repeats . External to SCCpbp4, SCC-CI contains a second pair of ccrAB genes (allotype 4), three IS431 elements, and genes mediating resistance to heavy metals . Genes mediating restriction-modification that may facilitate horizontal transfer are also present within SCC-CI, both within and outside SCCpbp4. Several novel arrangements of the SCC direct and inverted repeats were identified . Several long stretches of homology with other SCCs were found within and outside SCCpbp4 . In view of the fact that SCC-CI was found in a commensal species, it may represent a reservoir for sequences involved in genetic shuffling between staphylococci and may contribute to the diversity found in SCC elements . A Genetically Economical Family of Plasmid-Encoded Transcriptional Repressors Involved in Control of Plasmid Copy Number. Gloria del Solar, 2002. Characterization of Hybrid Toluate and Benzoate Dioxygenases. Yong Ge, 2003.Toluate dioxygenase of Pseudomonas putida mt-2 (TADOmt2) and benzoate dioxygenase of Acinetobacter calcoaceticus ADP1 (BADOADP1) catalyze the 1,2-dihydroxylation of different ranges of benzoates . The catalytic component of these enzymes is an oxygenase consisting of two subunits . To investigate the structural determinants of substrate specificity in these ring-hydroxylating dioxygenases, hybrid oxygenases consisting of the  subunit of one enzyme and the ß subunit of the other were prepared, and their respective specificities were compared to those of the parent enzymes . Reconstituted BADOADP1 utilized four of the seven tested benzoates in the following order of apparent specificity: benzoate > 3-methylbenzoate > 3-chlorobenzoate > 2-methylbenzoate . This is a significantly narrower apparent specificity than for TADOmt2 (3-methylbenzoate > benzoate
 3-chlorobenzoate > 4-methylbenzoate
4-chlorobenzoate >> 2-methylbenzoate
2-chlorobenzoate [Y . Ge, F . H . Vaillancourt, N . Y . Agar, and L . D . Eltis, J . Bacteriol . 184:4096-4103, 2002]) . The apparent substrate specificity of the
BßT hybrid oxygenase for these benzoates corresponded to that of BADOADP1, the parent from which the
subunit originated . In contrast, the apparent substrate specificity of the
TßB hybrid oxygenase differed slightly from that of TADOmt2 (3-chlorobenzoate > 3-methylbenzoate > benzoate
4-methylbenzoate > 4-chlorobenzoate > 2-methylbenzoate > 2-chlorobenzoate) . Moreover, the
TßB hybrid catalyzed the 1,6-dihydroxylation of 2-methylbenzoate, not the 1,2-dihydroxylation catalyzed by the TADOmt2 parent . Finally, the turnover of this ortho-substituted benzoate was much better coupled to O2 utilization in the hybrid than in the parent . Overall, these results support the notion that the
subunit harbors the principal determinants of specificity in ring-hydroxylating dioxygenases . However, they also demonstrate that the ß subunit contributes significantly to the enzyme's function .
Rhamnogalacturonate Lyase RhiE Is Secreted by the Out System in Erwinia chrysanthemi. Minna Laatu, 2003.Supernatants of rhamnose-induced Erwinia chrysanthemi strain 3937 cultures contain a principal secreted protein named RhiE . A rhiE mutant has been found among a set of rhamnose-induced MudI1681 lacZ fusions . RhiE is a 62-kDa protein that has rhamnogalacturonate lyase activity on rhamnogalacturonan I (RG-I) . It does not require a divalent cation for its activity and has an optimal pH of 6.0 . rhiE expression is strongly induced in the presence of rhamnose but is also regulated by PecT and Crp, two regulators of the transcription of pectinolytic enzyme genes . RhiE is secreted through the type II Out secretion pathway . RhiE has no disulfide bond . The absence of RhiE secretion in a dsb mutant indicated that disulfide bond formation is required for the biogenesis of the secretion apparatus . RhiE was searched for in several E . chrysanthemi strains by using antibodies, and it was found to be present in one-third of the strains tested . However, the reduced virulence of the rhiE mutant indicates that degradation of the RG-I region of pectin is important for full virulence of E . chrysanthemi .
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