IDENTIFICATION AND CHARACTERIZATION OF A G-PROTEIN-COUPLED RECEPTOR HOMOLOG ENCODED BY MURINE CYTOMEGALOVIRUS

This report describes the identification of a murine cytomegalovirus ( MCMV) G protein-coupled receptor (GCR) homolog. This open reading fram e (M33) is most closely related to, and collinear with, human cytomega lovirus UL33, and homologs are also present in human herpesvirus 6 and 7 (U12 for both viruses). Conserved counterparts in the sequenced alp ha- or gammaherpesviruses have not been identified to date, suggesting that these genes encode proteins which are important for the biologic al characteristics of betaherpesviruses. We have detected transcripts for both UL33 and M33 as early as 3 or 4 h postinfection, and these re appear at late times. In addition, we have identified N-terminal splic ing for both the UL33 and M33 RNA transcripts. For both open reading f rames, splicing results in the introduction of amino acids which are h ighly conserved among known GCRs. To characterise the function of the M33 in the natural host, two independent MCMV recombinant viruses were prepared, each of which possesses an M33 open reading frame which has been disrupted with the beta-galactosidase gene. While the recombinan t M33 null viruses showed no phenotypic differences in replication fro m wild-type MCMV in primary mouse embryo fibroblasts in vitro, they sh owed severely restricted growth in the salivary glands of infected mic e. These data suggest that M33 plays an important role in vivo, in par ticular in the dissemination to or replication in the salivary gland, and provide the first evidence for the function of a viral GCR homolog in vivo.