Murine gammaherpesvirus-68 encodes homologues of thymidine kinase and glycoprotein H: sequence, expression, and characterization of pyrimidine kinase activity.

We have sequenced a 4.5-kb fragment of DNA spanning the junction of the BamHI D and E fragments of murine gammaherpesvirus-68 (MHV-68). This sequence was found to code for two major open reading frames (orfs) of 1934 and 2192 bp which showed significant homology to the thymidine kinase (TK) and glycoprotein H (gH) sequences of other gammaherpesviruses. Upstream from the TK gene another orf was found which showed amino acid sequence homology to the HSV1 UL24 gene. Analysis of the 1934-bp orf revealed the presence of all six of the recognized sites that are conserved between herpesvirus TKs although, uniquely among sequenced herpesvirus TK enzymes, MHV-68 lacks the consensus nucleotide binding site GXXGXGK, the second glycine being replaced by alanine. The MHV-68 TK has a predicted M(r) of 68,443, while the gH is predicted to have a M(r) of 82,890. Northern blot analysis showed an early TK message of 2.6 kb and a late gH-specific message of 2.5 kb. Both TK and gH probes detected a 4.3-kb late message, implying that this late message spans gH and TK. The TK coding sequence was expressed using an in vitro transcription translation system and was shown to encode functional TK activity.