MAPPING AND TRANSCRIPTIONAL ANALYSIS OF THE MURINE CYTOMEGALOVIRUS HOMOLOG OF THE HUMAN CYTOMEGALOVIRUS UL103 OPEN READING FRAME

Murine cytomegalovirus (MCMV) has been widely used as a model for huma n cytomegalovirus (HCMV) infection since the two viruses share many bi ological and pathogenic properties. To further evaluate the similariti es in the genomes of these viruses we have sought to identify MCMV gen es that encode immunoreactive proteins by screening a lambda gt11 cDNA library with anti-MCMV monoclonal antibodies (MAb). Clone 430, identi fied on the basis of its reactivity with the MAb 6/20/1, was completel y sequenced and shown to encode the MCMV homologue of the HCMV UL103 o pen reading frame (ORF). This ORF is encoded by a 1.1-kb transcript th at is expressed at late times following infection. Sequencing of the c DNA also revealed the presence of two incomplete ORFs encoding the hom ologues of the HCMV UL102 and 104 ORFs. These ORFs are encoded by a 2. 4-kb leaky late transcript and a 3.0-kb late transcript, respectively. Together these ORFs constitute part of a block of genes conserved in all herpesviruses, and in the MCMV and HCMV genomes this block of gene s shows striking positional homology. The high degree of homology betw een HCMV and MCMV ORFs, at both the nucleotide and amino acid levels, plus the growing evidence of conservation in gene order between the tw o genomes suggests that the two viruses are very similar at the molecu lar level. (C) 1994 Academic Press, Inc.