This domain is found at the C terminus of adenylosuccinate lyase (ASL; PurB in Escherichia coli). It has been identified in bacteria, eukaryotes and archaea and is found together with the lyase domain . ASL catalyses the cleavage of succinylaminoimidazole carboxamide ribotide to aminoimidazole carboxamide ribotide and fumarate and the cleavage of adenylosuccinate to adenylate and fumarate [].
This family includes N6-succino-2-amino-2'-deoxyadenylate synthase PurZ from phages. It is involved in the synthesis of the atypical nucleotide dZTP (2-amino-2'-deoxyadenosine-5'-triphosphate) and in the synthesis of N6-succino-2-amino-2'-deoxyadenylate, which undergoes defumarylation and phosphorylation respectively by host PurB and guanylate/nucleoside diphosphate kinases to give dZTP (2-amino-2'-deoxyadenosine-5'-triphosphate). dZTP is integrated into the viral genome instead of adenine by the viral polymerase. This Z-base probably completely replaces adenosine and forms a triple bond to the opposite T-base. The resulting non-standard viral DNA is called Z-genome. The chemically modified DNA is probably harder for the host bacteria to digest with nucleases or restriction enzymes [, ].
