title: Proteolytically induced changes in the molecular form of the carbamyl phosphate synthetase-uracil-aspartate transcarbamylase complex coded for by the URA2 locus in Saccharomyces cerevisiae.
abstract: When a uracil-auxotrophic yeast strain is grown under uracil-limiting conditions, the aspartate transcarbamylase activity found in crude extracts shows a variation in sensitivity to feedback inhibition by uridine 5'-triphosphate. In this study we correlated this variation with changes in the molecular form of the carbamyl phosphate synthetase-uracil-aspartate transcarbamylase complex. Carbamyl phosphate synthetase-uracil (molecular weight, 240,000) and uridine 5'-triphosphate-insensitive aspartate transcarbamylase (molecular weight, 140,000) were present separately in extracts from cells collected in the early exponential phase; this was in contrast to the presence of a single high-molecular-weight form (molecular weight, about 900,000) bearing both activities in extracts from stationary-phase cells. The lack of sensitivity to uridine 5'-triphosphate by aspartate transcarbamylase was delayed by adding uridine 5'-triphosphate before cell disruption and was prevented completely by adding phenylmethylsulfonyl fluoride. Thus, this event was attributed to a transient serine protease activity detected only in early exponential-phase cell extracts. However, even in the presence of phenylmethylsulfonyl fluoride, a sucrose density gradient analysis in the absence of uridine 5'-triphosphate revealed a change in the aggregation state of the complex which might have occurred in vivo. None of these events was observed in extracts from cells that lacked protease B activity (strain HP232-2B).
mesh_terms: D001221:Aspartate Carbamoyltransferase / Q000235:genetics / Q000378:metabolism*; D002223:Carbamoyl-Phosphate Synthase (Glutamine-Hydrolyzing) / Q000235:genetics / Q000378:metabolism*; D010450:Endopeptidases / Q000378:metabolism; D008025:Ligases / Q000378:metabolism*; D009097:Multienzyme Complexes / Q000235:genetics / Q000378:metabolism*; D010447:Peptide Hydrolases / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000235:genetics; D012697:Serine Endopeptidases; D014498:Uracil / Q000378:metabolism; D014544:Uridine Triphosphate / Q000494:pharmacology; D029701:Saccharomyces cerevisiae Proteins
chemical_list: D001221:Aspartate Carbamoyltransferase; D002223:Carbamoyl-Phosphate Synthase (Glutamine-Hydrolyzing); D010450:Endopeptidases; D008025:Ligases; D009097:Multienzyme Complexes; D010447:Peptide Hydrolases; D012697:Serine Endopeptidases; D014498:Uracil; D014544:Uridine Triphosphate; C023302:yeast proteinase B; D029701:Saccharomyces cerevisiae Proteins