GENOMIC ORGANIZATION OF THE MYCOBACTERIAL SIGMA-GENE-CLUSTER

We have previously described sigma(A) and sigma(B) and their structura l genes, mysA and mysB, respectively, in Mycobacterium smegmatis. We h ave now sequenced the corresponding regions in the M. tuberculosis and M. leprae chromosomes, and have found the two homologous genes. The c hromosomal linkage and the deduced amino acid (aa) sequences of the tw o genes show very high similarity in the three species of mycobacteria . We also report the finding of two other open reading frames (ORF) in these clusters. orfX, which has an unknown function, is located betwe en mysA and mysB. The other ORF, located downstream from mysB, encodes a homolog of DtxR, the iron regulatory protein from Corynebacterium d iphtheriae (Cd).