5'-Phosphoribosyl-5-aminoimidazole (AIR) carboxylase (EC 4.1.1.21) catalyzes step 6, the carboxylation of AIR to 5'-phosphoribosyl-5-aminoimidazole-4-carboxylic acid, in the de novo biosynthesis of purine nucleotides. As deduced from the DNA sequence of restriction fragments encoding AIR carboxylase and supported by maxicell analyses, AIR carboxylase was found to be composed of two nonidentical subunits. In agreement with established complementation data, the catalytic subunit (deduced Mr, 17,782) was encoded by the purE gene, while the CO2-binding subunit (deduced Mr, 39,385) was encoded by the purK gene. These two genes formed an operon in which the termination codon of the purE gene overlapped the initiation codon of the purK gene. The 5' end of the purEK mRNA was determined by mung bean nuclease mapping and was located 41 nucleotides upstream of the proposed initiation codon. The purEK operon is regulated by the purR gene product, and a purR regulatory-protein-binding site related to the sequences found in other pur loci was identified in the purEK operon control region.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.