This protein is found in bacteria. Proteins in this family are typically between 136 to 150 amino acids in length. The opportunistic pathogen Mycobacterium smegmatis is resistant to rifampin because of the presence of a chromosomally encoded rifampin ADP-ribosyltransferase (Arr-ms). Arr-ms is a small enzyme whose activity thus renders rifamycin antibiotics ineffective [2].

1: Rifaximin pharmacology and clinical implications. Ojetti V, Lauritano EC, Barbaro F, Migneco A, Ainora ME, Fontana L, Gabrielli M, Gasbarrini A; Expert Opin Drug Metab Toxicol. 2009;5:675-682. PMID:19442033

2: Rifamycin antibiotic resistance by ADP-ribosylation: Structure and diversity of Arr. Baysarowich J, Koteva K, Hughes DW, Ejim L, Griffiths E, Zhang K, Junop M, Wright GD; Proc Natl Acad Sci U S A. 2008;105:4886-4891. PMID:18349144