Aspartate carbamoyltransferase catalyzes the conversion of aspartate and carbamoyl phosphate to carbamoylaspartate, the second step in the de novo biosynthesis of pyrimidine nucleotides. In prokaryotes ATCase consists of two subunits: a catalytic chain and a regulatory chain, while in eukaryotes it is a domain in a multi- functional enzyme (called URA2 in yeast, rudimentary in Drosophila, and CAD in mammals) that also catalyzes other steps of the biosynthesis of pyrimidines.

It has been shown that it's evolutionary related to ornithine carbamoyltransferase (EC 2.1.3.3). The predicted secondary structure of both enzymes are similar and there are some regions of sequence similarities. One of these regions includes three residues which have been shown, by crystallographic studies, to be implicated in binding the phosphoryl group of carbamoyl phosphate. This region has been selected as a signature for these enzymes.