This domain, formerly known as DUF2337, is the anti-sigma-K factor, RskA. In Mycobacterium tuberculosis the protein positively regulates expression of the antigenic proteins MPB70 and MPB83 [1].

1: Mutations in Mycobacterium tuberculosis Rv0444c, the gene encoding anti-SigK, explain high level expression of MPB70 and MPB83 in Mycobacterium bovis. Said-Salim B, Mostowy S, Kristof AS, Behr MA; Mol Microbiol. 2006;62:1251-1263. PMID:17064366