Sequence analysis of the UL39, UL38, and UL37 homologues of bovine herpesvirus 1 and expression studies of UL40 and UL39, the subunits of ribonucleotide reductase.

We sequenced the region of the bovine herpesvirus type 1 (BHV-1) genome corresponding to map units 0.172-0.230 (7964 bp), representing the UL39, UL38, and UL37 homologues of herpes simplex virus which encode the large subunit of ribonucleotide reductase (RR) and components of the viral capsid and the tegument, respectively. To discriminate between two potential initiator AUGs of the UL39 gene, the 5' end of the mRNA was mapped by S1 nuclease protection assays. Comparison of the amino acid sequences of the three BHV-1 proteins with analogous polypeptides from several other herpesviruses revealed significant levels of homology. We also compared the expression kinetics of the large (R1, UL39) versus the small (R2, UL40) RR subunits during the course of in vitro BHV-1 infection by Western blotting using specifically developed and calibrated antisera. Our results show that the R1 protein was synthesized earlier than its R2 counterpart. Moreover, the R1 protein accumulated to a higher level than the R2 protein even though the R2 transcript was in greater abundance than the R1 mRNA. This is discussed with regard to the translational efficiency of their transcripts.