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sigA is an essential gene in Mycobacterium smegmatis
Author(s) -
Gomez Manuel,
Doukhan Laurence,
Nair Gopalan,
Smith Issar
Publication year - 1998
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1046/j.1365-2958.1998.00960.x
Subject(s) - mycobacterium smegmatis , biology , sigma factor , streptomyces coelicolor , virulence factor , virulence , microbiology and biotechnology , gene , mycobacterium , mycobacterium bovis , genetics , rpos , locus (genetics) , gene expression , mycobacterium tuberculosis , mutant , bacteria , promoter , medicine , tuberculosis , pathology
sigA encodes a σ factor of the σ 70 family, σ A , that is found in all mycobacterial species. As σ A shows high similarity to the primary σ factor in Streptomyces coelicolor , it was postulated that σ A has the same role in mycobacteria. However, a point mutation in sigA , resulting in the replacement of arginine 522 by histidine, was found responsible for the attenuated virulence of the Mycobacterium bovis strain ATCC 35721. This raised the possibility that σ A was an alternative σ factor specifically required for virulence gene expression. In this work, we show that sigA can not be disrupted in Mycobacterium smegmatis unless an extra copy of the gene is provided at another chromosomal site, which demonstrates that sigA is essential. To characterize the pattern of sigA expression during exponential and stationary phase in M. smegmatis , we measured the β‐galactosidase activity in a strain carrying a sigA–lacZ transcriptional fusion and monitored σ A levels using Western blotting. Our results indicate that sigA is expressed throughout the growth of the culture. The essential character of sigA and its pattern of expression corroborate the hypothesis that sigA codes for the primary σ factor in M. smegmatis and, most likely, in all mycobacteria.