RESUMO
Thiol-disulphide exchanges are involved in many important biological processes; they are normally regulated by the glutaredoxin and thioredoxin systems. The thioredoxin system (TX) is composed of thioredoxin (TrxA) and thioredoxin reductase (TrxB) and requires NADPH as a cofactor. The thioredoxin genes trxA and trxB of Mycobacterium smegmatis mc2(6) were cloned and sequenced. The complete nucleotide sequences revealed that the TX genes of M. smegmatis were clustered, similar to the organization of trxA and trxB of S. clavuligerus, M. tuberculosis and M. leprae. Alignment with the M. tuberculosis and M. leprae protein sequences showed that the deduced amino acid sequences for M. smegmatis trxA and trxB have a very high degree of similarity. Sequence alignments and phylogenetic analysis of known TrxAs and TrxBs clearly identify the two gene products of M. smegmatis as members of the TX family grouped with other mycobacteria.