Cloning of a full-length cDNA encoding bovine thymus poly(ADP-ribose) synthetase: evolutionarily conserved segments and their potential functions

The primary structure of bovine thymus poly(ADP-ribose) synthetase, as deduced from the nucleotide sequence of a cloned cDNA, indicated that this enzyme is composed of 1016 amino acids (aa) with an M r of 113481. An abundance of Lys and Arg residues was in accord with the known basic nature of this protein. A comparison with reported sequences of human counterparts revealed: ( 1 ) three functional domains separated by partial proteolysis, i.e., DNA-binding (N-terminal), auto-modification (central), and NAD-binding (C-terminal) domains, have, in this order, increasing degrees of homology; ( 2 ) the DNA-binding domain is composed of two distinct regions: one, less conserved, containing zinc-binding fingers and the other, more conserved, containing helix-turn-helix motifs; ( 3 ) all Glu and Asp residues in the automodification domain are conserved; and ( 4 ) a 78-aa stretch encompassing the nucleotide-binding fold in the NAD-binding domain is completely conserved. These results are compatible with specific features of each domain, i.e., complex DNA-enzyme interactions, multiple automodification at acidic aa residues, and a stringent specificity for the substrate, NAD.