title: Mycobacterium smegmatis whmD and its homologue Mycobacterium tuberculosis whiB2 are functionally equivalent.
abstract: Mycobacterium smegmatis whmD is is an essential gene involved in cell division. This paper shows that whmD and its homologue whiB2 in Mycobacterium tuberculosis are functionally equivalent. The genes are syntenous, and share significant homology in both their coding and non-coding DNA sequences. Transcription site mapping showed that the two genes possess near-identical promoter elements, and they displayed comparable promoter strengths in a reporter gene assay. The two proteins show near identity in their C-terminus, and polyclonal antiserum to WhmD specifically cross-reacts with a approximately 15 kDa band in M. tuberculosis lysates. Following overexpression of sense and anti-sense constructs in their cognate mycobacterial hosts, whiB2 and whmD transformants displayed a small-colony phenotype, exhibited filamentation, and showed a reduction in viability. These observations reveal that the two proteins are functionally homologous and that their intracellular concentration is critical for septation in mycobacteria. Colonies of M. tuberculosis overexpressing whiB2 were spherical and glossy, suggesting a change in composition of the cell envelope. Filaments of the conditionally complemented M. smegmatis whmD mutant were non-acid-fast, also indicating changes in characteristics of surface lipids. M. smegmatis transformants carrying a whmD-gfp fusion showed a diffuse pattern of fluorescence, consistent with the putative role of WhmD as a regulator. These observations strongly suggest that M. tuberculosis whiB2 is an essential gene and its protein product in all likelihood regulates the expression of genes involved in the cell division cascade.
authors.affiliation: Department of Medicine, Johns Hopkins University, CRB2, Room 1.08, 1550 Orleans Street, Baltimore, MD 21231-1044, USA.
authors.forename: Tirumalai R
authors.initials: TR
authors.lastname: Raghunand
authors.affiliation: Department of Medicine, Johns Hopkins University, CRB2, Room 1.08, 1550 Orleans Street, Baltimore, MD 21231-1044, USA.
authors.forename: William R
authors.initials: WR
authors.lastname: Bishai
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism*; D001483:Base Sequence; D003429:Cross Reactions; D004269:DNA, Bacterial / Q000032:analysis; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D020043:Genes, Essential; D017930:Genes, Reporter; D005816:Genetic Complementation Test; D049452:Green Fluorescent Proteins / Q000378:metabolism; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009154:Mutation; D011401:Promoter Regions, Genetic; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D017422:Sequence Analysis, DNA; D012689:Sequence Homology, Nucleic Acid; D026801:Synteny; D014170:Transformation, Genetic; D001616:beta-Galactosidase / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D011993:Recombinant Fusion Proteins; C412372:WhmD protein, Mycobacterium smegmatis; D049452:Green Fluorescent Proteins; D001616:beta-Galactosidase