Specific inhibition of herpesvirus ribonucleotide reductase by a nonapeptide derived from the carboxy terminus of subunit 2

Ribonucleotide reductase, an essential enzyme for the synthesis of deoxyribonucleotides, is formed by the association of two non-identical subunits in almost all prokaryotic and eukaryotic cells 1 . The same model probably holds for the herpes simplex virus (HSV)-encoded ribonucleotide reductase 2–6 ; two polypeptides of relative molecular mass 136,000 (136K; H1) and 40K (H2) (referred to elsewhere as RR 1 and RR 2 ; see for example, Dutia et al. 26 ) have been associated with the viral enzyme by both genetic 7,8 and immunological 9–11 studies. Furthermore, DNA sequence analyses have shown significant stretches of amino-acid homology between these viral polypeptides and those of, respectively, subunit 1 (ref. 12) and subunit 2 (ref. 13) of the Escherichia coli and mammalian enzymes. To assess the involvement of the 40K polypeptide in reductase activity, we synthesized a nonapeptide corresponding to the sequence of its carboxy terminus with the intention of raising neutralizing antibodies specific for the viral activity (E.A.C. et al. , in preparation). We report here the unexpected finding that the nonapeptide itself specifically inhibits the HSV ribonucleotide reductase activity in a reversible, non-competitive manner, and we suggest that it does this by impairment of the correct association of the two subunits. This phenomenon emphasizes the potential usefulness of synthetic peptides in probing critical sites involved in macromolecular interactions.