Fig. 1.

Biosynthesis of arginine and pyrimidines. The names of structural genes encoding the enzymes catalyzing the different steps of de novo arginine and pyrimidine synthesis are indicated as follows: argA (N-acetylglutamate synthase), argB (N-acetylglutamate kinase), argC (N-acetylglutamylphosphate reductase), argD (N-acetylornithine transaminase), argE (N-acetylornithinase), argF and argI (ornithine transcarbamylase, two isoenzymes), argG (argininosuccinate synthetase), argH (argininosuccinase), carAB (carbamoylphosphate synthase), pyrBI (aspartate transcarbamylase with pyrB encoded catalytic and pyrI encoded regulatory subunit), pyrC (dihydroorotase), pyrD (dihydroorotate dehydrogenase), pyrE (orotate phophoribosyltransferase), pyrF (orotidine-5′-phosphate decarboxylase), pyrH (UMP kinase), pyrG (CTP-synthase)