Identification and characterization of the protein kinase activity associated with the large subunit of the herpes simplex virus type 2 ribonucleotide reductase and domain mapping of the multi-functional protein

Abstract

The transforming region of the herpes simplex virus type 2 (HSV-2) genome encodes a 140 kDa protein, designated ICP10, which was previously demonstrated to be the large subunit of the viral ribonucleotide reductase (RR1) and to share identity with the cervical cancer associated antigen AG-4. The present work was initiated to further characterize the biochemical and functional nature of ICP10 and to elucidate its role, if any, in the induction of neoplastic transformation. Combining computer assisted sequence analyses with conventional biochemical and molecular techniques, ICP10 is demonstrated to possess multiple functionally distinct domains. Most significantly, the amino terminal one-third of ICP10, previously shown to be unique to HSV, possesses protein kinase (PK) activity, a transmembrane helical segment and an extracellular modulatory domain analogous to growth factor receptor kinases. Analysis of the RR activity reveals that leucine-rich stretch of amino acids representing the junction between the PK and RR domains is critical for association of the two virally encoded RR subunits and a previously uncharacterized cellular 180 kDa protein that functions to stabilize the RR activity. It is proposed that the ICP10 protein represents a chimera between a cellular receptor kinase-related oncoprotein and the HSV-2 RR1. Stabilization of the RR active complex may be one factor that has favored conservation of this union.