Pupylation is a novel protein modification system found in some bacteria [1]. This family of proteins are the enzyme that can conjugate proteins of the Pup family to lysine residues in target proteins marking them for degradation. The archetypal protein in this family is PafA (proteasome accessory factor) from Mycobacterium tuberculosis [2]. It has been suggested that these proteins are related to gamma-glutamyl-cysteine synthetases [1].

1: Unraveling the biochemistry and provenance of pupylation: a prokaryotic analog of ubiquitination. Iyer LM, Burroughs AM, Aravind L; Biol Direct. 2008;3:45. PMID:18980670

2: Ubiquitin-like protein involved in the proteasome pathway of Mycobacterium tuberculosis. Pearce MJ, Mintseris J, Ferreyra J, Gygi SP, Darwin KH; Science. 2008;322:1104-1107. PMID:18832610