THE R33 G-PROTEIN-COUPLED RECEPTOR GENE OF RAT CYTOMEGALOVIRUS PLAYS AN ESSENTIAL ROLE IN THE PATHOGENESIS OF VIRAL-INFECTION

We have identified a rat cytomegalovirus (RCMV) gene that encodes a G- protein-coupled receptor (GCR) homolog, This gene (R33) belongs to a f amily that includes the human cytomegalovirus UL33 gene, R33 was found to be transcribed during the late phase of RCMV infection in rat embr yo fibroblasts. Unlike the mRNAs from all the other members of the UL3 3 family that have been studied to date, the R33 mRNA is not spliced, To study the function of the R33 gene, we constructed an RCMV strain i n which the R33 open reading frame is disrupted. The mutant strain (RC MV Delta R33) did not show differences in replication from wild-type R CMV upon infection of several rat cell types in vitro. However, marked differences were seen between the mutant and wild-type strain in the pathogenesis of infection in immunocompromised rats, First, the mutant strain induced a significantly lower mortality than the wild-type vir us did. Second, in contrast to wild-type RCMV, the mutant strain did n ot efficiently replicate in the salivary gland epithelial cells of imm unocompromised rats, Although viral DNA was detected in salivary gland s of RCMV Delta R33-infected rats up to 14 days postinfection, it coul d net be detected at later time points. This indicates that although t he strain with R33 deleted is probably transported to the salivary gla nds in a similar fashion to that for wild-type virus, the mutant virus is not able to either enter or replicate in salivary gland epithelial cells, We conclude that the RCMV R33 gene plays a vital role in the p athogenesis of infection.