RESUMO
We have previously described sigma A and sigma B and their structural genes, mysA and mysB, respectively, in Mycobacterium smegmatis. We have now sequenced the corresponding regions in the M. tuberculosis and M. leprae chromosomes, and have found the two homologous genes. The chromosomal linkage and the deduced amino acid (aa) sequences of the two 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 between mysA and mysB. The other ORF, located downstream from mysB, encodes a homolog of DtxR, the iron regulatory protein from Corynebacterium diphtheriae (Cd).
Assuntos
Genoma Bacteriano , Mycobacterium leprae/genética , Mycobacterium tuberculosis/genética , Fator sigma/genética , Sequência de Aminoácidos , Sequência de Bases , Mapeamento Cromossômico , Dados de Sequência Molecular , Família Multigênica , Alinhamento de SequênciaRESUMO
A search for Mycobacterium smegmatis genes showing similarity to the conserved family encoding major sigma factors in diverse prokaryotes has identified two such determinants. Both genes are expressed in exponentially growing cells, as judged by Western immunoassays. A series of chromatographic steps was used to purify M. smegmatis RNA polymerase holoenzyme and it was shown that its ability to initiate in vitro transcription with a heterologous Bacillus subtilis promoter is dependent on the presence of these sigma factor(s). Reconstitution of specific in vitro transcription activity was obtained upon mixing of M. smegmatis core RNA polymerase with the major sigma factor of Bacillus subtilis. We also demonstrated in vitro transcription of the M. smegmatis rrnB promoter by the M. smegmatis RNA polymerase. Significantly, highly active B. subtilis RNA polymerase holoenzyme was unable to transcribe this gene.