Although the guinea-pig cytomegalovirus (GPCMV) displays a similar pathogenesis to human cytomegalovirus (HCMV), there have unfortunately been few molecular analyses of the GPCMV genome to date. The guinea-pig has proved useful for the testing of drugs active against CMV infection, and insights derived from characterization of the specific virally encoded molecular targets of antiviral therapies would allow this model system to be more fully developed. Because the DNA polymerase serves as an important target for nucleoside antiviral agents active against herpesviruses, experiments were undertaken to identify, clone and sequence the GPCMV DNA polymerase gene (pol). A 3285 bp ORF capable of encoding a 1094 amino acid protein was identified spanning portions of the HindIII Q and P fragments of the genome. This ORF contained extensive homology to other herpesvirus DNA pol genes. Northern blot analyses identified two 3' coterminal pol-specific mRNAs of 3.9 and 1.9 kb at early times post-infection. Primer extension and nuclease protection analyses mapped the 5' end of the 3.9 kb transcript to a site 275 bases upstream of the pol initiation codon. Comparison of the GPCMV pol-encoded sequence to those of other herpesvirus polymerases identified non-conservative amino acid substitutions in a domain involved in substrate recognition.