Subunit of the carbamoyl-phosphate synthetase (CPS) composed of a small chain CARA/VEN6 and a large chain CARB/VEN3. Involved in arginine biosynthesis. Required for mesophyll development. 2 ATP + H2O + hydrogencarbonate + L-glutamine = 2 ADP + carbamoyl phosphate + 2 H(+) + L-glutamate + phosphate Amino-acid biosynthesis; L-arginine biosynthesis; carbamoyl phosphate from bicarbonate: step 1/1. Pyrimidine metabolism; UMP biosynthesis via de novo pathway; (S)-dihydroorotate from bicarbonate: step 1/3. Composed of two chains; the small (or glutamine) chain promotes the hydrolysis of glutamine to ammonia, which is used by the large (or ammonia) chain to synthesize carbamoyl phosphate. A number of isoforms are produced. According to EST sequences. By phosphate starvation in shoot. Reduced plant size. Reticulate leaves with reduced number of palissade mesophyll cells. The ven6-1 phenotype is rescued by exogenous application of citrulline, an arginine precursor. Belongs to the CarA family. Truncated N-terminus.