DNA-SEQUENCE AND TRANSCRIPTIONAL ANALYSIS OF THE GLYCOPROTEIN-M GENE OF MURINE CYTOMEGALOVIRUS

We have characterized the gene encoding the murine cytomegalovirus (MC MV) homologue of the human cytomegalovirus (HCMV) UL100 open reading f rame (ORF) that encodes the HCMV glycoprotein M (gM) molecule. It was identified based on its collinearity with MCMV homologues of the HCMV UL99, UL102, UL103 and UL104 ORFs which lie in the HindIII G fragment of the K181 strain of MCMV. Sequencing of a 2.3 kb EcoRI-BamHI subfrag ment of the EcoRI G fragment adjacent to the EcoRI A fragment revealed the presence of the complete MCMV gM ORF and two incomplete ORFs, whi ch corresponded to homologues of HCMV UL99 and UL102. The MCMV gM ORF consists of 1059 nucleotides and is expressed as a 1.2 kb transcript a t late times post-infection. To precisely characterize the gM transcri pt, the 5' and 3' ends were mapped. It was found that the transcript i nitiates at nucleotides 740 or 745, and that the site of polyadenylati on at nucleotide 1961 occurs downstream of the second potential polyad enylation signal located at nucleotide 1934. Based on these findings t he MCMV gM is predicted to consist of 353 residues and when compared w ith HCMV gM has a 47 % level of identity. Of great interest is the fin ding that the MCMV gM amino acid sequence is completely conserved amon g six isolates of MCMV that had been shown to exhibit considerable var iation both in the MCMV glycoprotein B and the immediate-early 1 gene- encoded pp89 molecule. Thus, this glycoprotein appears to be antigenic ally conserved.