Evolution of the mycobacterial SigK regulon

Department of Medicine, McGill University, Montreal, QC, H3G 1A4, Canada

^* To whom correspondence should be addressed. Email: marcel.behr{at}mcgill.ca.

	Abstract

Previous studies have established that M. tuberculosis complex exhibits variable production of the antigenic proteins, MPT70 and MPT83, due to mutations in their positive regulator, SigK (Sigma Factor K), and their negative regulator, RskA (Regulator of Sigma K). To further understand this highly specific SigK-controlled regulon, we have undertaken evolutionary studies to determine the presence of homologues of SigK-regulated genes in other organisms, and to predict its transcriptional network. Evolutionary analysis indicates that the positive and negative regulators are conserved across many organisms, but that the genes under their control are variable. Moreover, the addition, loss and movement of various genes in the mpt70/83 locus suggest that these genes are unlikely to be co-transcribed. To test predictions from sequence analysis, we have used promoter luciferase fusions and Northern blots to show that the majority of genes in this locus have their own promoters, of which a subset are SigK-regulated (mpt83, dipZ, mpt70 and Rv0449c). Next, we have shown that the intracellular inducibility of mpt70 and mpt83 is a conserved property, shared between M. tuberculosis and M. marinum. In addition, we have shown that SigK and RskA from an environmental mycobacterium (M. gilvum PYR-GCK) complemented the regulatory activity of M. tuberculosis sigK-rskA. Together, our data indicate that the regulatory system, SigK/RskA, is conserved across the Mycobacterium genus whereas the regulon under its control varies considerably across species.