E1_ThiF_like. Member of superfamily of activating enzymes (E1) of the ubiquitin-like proteins. The common reaction mechanism catalyzed by E1-like enzymes begins with a nucleophilic attack of the C-terminal carboxylate of the ubiquitin-like substrate, on the alpha-phosphate of an ATP molecule bound at the active site of the activating enzymes, leading to the formation of a high-energy acyladenylate intermediate and subsequently to the formation of a thiocarboxylate at the C termini of the substrate. The exact function of this family is unknown.