The herpes simplex virus type 1 ribonucleotide reductase is a tight complex of the type alpha 2 beta 2 composed of 40K and 140K proteins, of which the latter shows multiple forms due to proteolysis.

We have isolated two monospecific monoclonal mouse antibodies directed against the HSV-1 ribonucleotide reductase. When immobilized to Sepharose, both antibodies remove enzyme activity from solution. However, on immunoblots of crude extracts of HSV-1-infected cells, one antibody only detects a 140K protein and the other antibody only a 40K protein. Neither antibody recognizes the cellular ribonucleotide reductase or the related pseudorabies virus-induced enzyme. Therefore, our data strongly suggest that the HSV-1 ribonucleotide reductase consists of a 140K and a 40K protein. The 140K protein is sequentially degraded to 110K, 93K, and 81K proteins by a Vero cell-specific, N alpha-p-tosyl-L-lysine chloromethyl ketone-sensitive protease. Of the different proteolytic products, at least the 93K species seems to be enzymatically active, suggesting that part of the 140K protein may have functions not related to ribonucleotide reduction. There is a very high affinity between the 140K and 40K proteins as evident from affinity chromatography on antibody-Sepharose and sedimentation velocity centrifugation in a glycerol gradient. The 140K and 40K proteins cosediment with the HSV-1 ribonucleotide reductase activity at 17 S. This indicates that the active form of the HSV-1 reductase consists of the 140K and 40K proteins forming a tight complex of the alpha 2 beta 2 type.