The complete DNA sequence of the Smith strain of murine cytomegalovirus (MCMV) was determined from virion DNA by using a whole-genome shotgun approach. The genome has an overall G؉C content of 58.7%, consists of 230,278 bp, and is arranged as a single unique sequence with short (31-bp) terminal direct repeats and several short internal repeats. Significant similarity to the genome of the sequenced human cytomegalovirus (HCMV) strain AD169 is evident, particularly for 78 open reading frames encoded by the central part of the genome. There is a very similar distribution of G؉C content across the two genomes. Sequences toward the ends of the MCMV genome encode tandem arrays of homologous glycoproteins (gps) arranged as two gene families. The left end encodes 15 gps that represent one family, and the right end encodes a different family of 11 gps. A homolog (m144) of cellular major histocompatibility complex (MHC) class I genes is located at the end of the genome opposite the HCMV MHC class I homolog (UL18). G protein-coupled receptor (GCR) homologs (M33 and M78) occur in positions congruent with two (UL33 and UL78) of the four putative HCMV GCR homologs. Counterparts of all of the known enzyme homologs in HCMV are present in the MCMV genome, including the phosphotransferase gene (M97), whose product phosphorylates ganciclovir in HCMVinfected cells, and the assembly protein (M80).

The principle by which mouse cytomegalovirus blocks antigen presentation in the MHC class I pathway was investigated. The responsible gene m152, encoding a type I transmembrane glycoprotein of 40 kDa, is a member of a gene family located in the right-hand terminal region of the 230 kb virus genome. Expression of m152 in murine and human cells arrested the export of mouse class I complexes from the ER-Golgi intermediate compartment/cis-Golgi compartment and inhibited lysis by cytotoxic T cells. The plasma membrane transport of human MHC class I molecules was not affected. The deletion of the cytoplasmic tail of gp40 did not lift its effect on class I molecule export, indicating that this protein differs in its functions from known immunosubversive viral gene products and represents a novel principle by which a herpesvirus shuts off MHC class I function.

Cellular infection by cytomegalovirus (CMV) is associated with very early G-protein-mediated signal transduction and reprogramming of gene expression. Here we investigated the involvement of human CMV (HCMV)-encoded US27, US28, and UL33 receptors as well as murine CMV-encoded M33 transmembrane (7TM) receptors in host cell signaling mechanisms. HCMV-encoded US27 did not show any constitutive activity in any of the studied signaling pathways; in contrast, US28 and M33 displayed ligand-independent, constitutive signaling through the G protein q (Gq)/phospholipase C pathway. In addition, M33 and US28 also activated the transcription factor NF-B as well as the cyclic AMP response element binding protein (CREB) in a ligand-independent, constitutive manner. The use of specific inhibitors indicated that the p38 mitogenactivated protein (MAP) kinase but not the extracellular signal-regulated kinase 1/2-MAP kinase pathway is involved in M33-and US28-mediated CREB activation but not NF-B activation. Interestingly, UL33-the HCMV-encoded structural homologue of M33-was only marginally constitutively active in the Gq/phospholipase C turnover and CREB activation assays and did not show any constitutive activity in the NF-B pathway, where M33 and US28 were highly active. Hence, CMVs appear to have conserved mechanisms for regulating host gene transcription, i.e., constitutive activation of certain kinases and transcription factors through the constitutive activities of 7TM proteins. These data, together with the previous identification of the incorporation of such proteins in the viral envelope, suggest that these proteins could be involved in the very early reprogramming of the host cell during viral infection.Cytomegaloviruses (CMVs) are widespread opportunistic pathogens that cause acute, latent, and chronic infections. Although the primary infection is asymptomatic in immunocompetent individuals, these viruses can cause a wide variety of diseases in immunocompromised hosts (2). One hallmark of human CMV (HCMV) infection of quiescent cells is the upregulation of many host cell proteins, including DNA replication enzymes and transcription factors, which are necessary for both viral gene expression and viral DNA replication. Interestingly, some of these cellular changes occur even before the activation of the immediate-early genes of the virus, and some of these changes are clearly associated with classical G-protein signaling pathways. For example, the exposure of human fibroblasts to HCMV is associated with a very rapid G-proteindependent increase in phospholipase C (PLC) activity, as reflected in the intracellular levels of diacylglycerol and inositol 1,4,5-triphosphate, as well as the rapid release of arachidonic acid metabolites (1).HCMV encodes four putative 7-transmembrane (7TM) Gprotein-coupled receptors, US27 and US28 (both HCMV specific) and UL33 and UL78 (both betaherpesvirus conserved) (11,20,31) (Fig. 1), with structural homology to chemokine receptors. So far, only US28 has been characterized pharmacologically an...

A mouse cytomegalovirus glycoprotein, gp34, forms a complex with folded class I MHC molecules in the ER which is not retained but is transported to the cell surface ing presentation of peptide by MHC class I molecules Maurits F.Kleijnen 1 , Johannes B.Huppa, (York et al., 1994;Früh et al., 1995; Hill et al., 1995). to the presence of a Gly-Ala repeat in EBNA-1 (Levitskaya et al., 1995). Human cytomegalovirus (HCMV) infection Pero Lucin