Transcriptional analysis of human cytomegalovirus and rat cytomegalovirus homologues of the M73/M73.5 spliced gene family

Previous analysis of the M73-to-m74/M75 intergenic region of murine cytomegalovirus (MCMV) identified a family of 3'-co-terminal spliced transcripts that includes M73 and M73.5. The current study investigated whether similar families of spliced genes also exist in the human CMV (HCMV) and rat CMV (RCMV) genomes. Northern blot, RT-PCR and RACE-PCR analysis of HCMV transcripts showed that while mRNAs from HCMV UL73 and a putative UL73.5 homologue were spliced and 3'-co-terminal, they were not 5'-co-terminal. In contrast, the spliced RCMV R73 and R73.5 transcripts were arranged in a similar manner to those in MCMV and found to be both 5' and 3'-co-terminal. In both the HCMV and RCMV genomes, additional non-coding spliced transcripts were found to originate from these regions. These results highlight that families of spliced transcripts coding for structural glycoproteins are likely to be a conserved feature of this region of betaherpesviral genomes.