UNIQUE GENE ORGANIZATION OF THIOREDOXIN AND THIOREDOXIN REDUCTASE IN MYCOBACTERIUM-LEPRAE

The thioredoxin system comprising thioredoxin (Trx), thioredoxin reduc tase (TR) and NADPH operates via redox-active disulphides and provides electrons for a wide variety of different metabolic processes in prok aryotic and eukaryotic cells. Thioredoxin is also a general protein di sulphide reductase involved in redox regulation. In bacteria, the Trx and TR proteins previously identified were encoded by separate genes ( trxA and trxB). In this study, we report a novel genomic organization of Tn and Trx in mycobacteria and show that at least three modes of or ganization of Tn and Trx genes can exist within a single bacterial gen us: (i) in the majority of mycobacterial strains the genes coding for Tn and Trx are located on separate sites of the genome; (ii) interesti ngly, in all pathogenic Mycobacterium tuberculosis complex mycobacteri a both genes are found on the same locus, overlapping in one nucleotid e; (iii) in the pathogen Mycobacterium leprae, TR and Trx are encoded by a single gene. Sequence analysis of the M. leprae gene demonstrated that the N-terminal part of the protein corresponds to Tn and the C-t erminal part to Trx. A corresponding single protein product of approxi mately 49 kDa was detected in cell extracts of M. leprae. These findin gs demonstrate the very unusual phenomenon of a single gene coding for both the substrate (thioredoxin) and the enzyme (thioredoxin reductas e), which seems to be unique to M. leprae.