. "The enzyme catalyzes the covalent attachment of the prokaryotic ubiquitin-like protein modifier Pup to the proteasomal substrate proteins, thereby targeting them for proteasomal degradation." . "This tagging system is termed pupylation." . "The ligation reaction involves the side-chain carboxylate of the C-terminal glutamate of Pup and the side-chain amino group of a substrate lysine." . "PafA is required to confer resistance against the lethal effects of reactive nitrogen intermediates (RNI), antimicrobial molecules produced by activated macrophages and other cell types." . . . "Pup--protein ligase" . "Pup-conjugating enzyme" . "ATP + [Pup] + [protein]-lysine = ADP + phosphate + [protein]-N-pupyllysine." .