Protein sequence comparisons show that the ‘pseudoproteases’ encoded by poxviruses and certain retroviruses belong to the deoxyuridine triphosphatase family

Amino acid sequence comparisons show extensive similarities among the deoxyuridine triphosphatases (dUTPases) of Escherichia coli and of herpesviruses, and the 'protease-like' or 'pseudoprotease' sequences encoded by certain retroviruses in the oncovirus and lentivirus families and by poxviruses. These relationships suggest strongly that the 'pseudoproteases' actually are dUTPases, and have not arisen by duplication of an oncovirus protease gene as had been suggested. The herpesvirus dUTPase sequences differ from the others in that they are longer (about 370 residues, against around 140) and one conserved element ('Motif 3') is displaced relative to its position in the other sequences; a model involving internal duplication of the herpesvirus gene can account effectively for these observations. Sequences closely similar to Motif 3 are also found in phosphofructokinases, where they form part of the active site and fructose phosphate binding structure; thus these sequences may represent a class of structural element generally involved in phosphate transfer to and from glycosides.