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Characterization of the thioredoxin system genes of Mycobacterium smegmatis Asano, Rumi Lynn


The thioredoxin system is composed of thioredoxin (TrxA), thioredoxin reductase (TrxB) and NADPH. Degenerate oligonucleotide primers were designed to detect, by polymerase chain reaction (PCR), trxA and trxB genes in M.smegmatis mc²6. The complete nucleotide sequence of the Mycobacterium smegmatis thioredoxin system genes were obtained and were found to be organized similarly to the trxA and trxB gene cluster of Streptomyces clavuligerus, M.tuberculosis and M.leprae. A 14 kDa protein in M.smegmatis lysates was identified by Western blot analysis using antiserum to E.coli TrxA. Analysis of the M.smegmatis trxA and trxB gene sequences by BLAST revealed a high identity with other thioredoxin system genes. Sequence alignment with the M.tuberculosis and M.leprae genes showed that the M.smegmatis trxA and trxB deduced amino acid sequences have a very high degree of similarity; 72.7% identity and 81.5% similarity to the 49 kDa fusion protein of M.leprae, and 76.6% identity and 85.4% similarity to M.tuberculosis, respectively. Sequence alignments and phylogenetic tree analysis of known TrxA's and TrxB's clearly identify the two genes of M.smegmatis as members of the thioredoxin system genes grouped with other Actinomycetes and more specifically, within a mycobacterial branch.

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