CHARACTERIZATION OF THE MAJOR LOCUS OF IMMEDIATE-EARLY GENES OF RAT CYTOMEGALOVIRUS

A major locus of rat cytomegalovirus (RCMV) immediate-early (IE) RNA t ranscription was identified. A cDNA library from rat embryo fibroblast s infected with RCMV under IE conditions was constructed and screened by using appropriate RCMV DNA probes, revealing at least two IE genes (IE1 and IE2) transcribed from this locus by differential splicing. Th e first three exons (the first is noncoding) are spliced to exon 4 to form IE1 and to exon 5 to form IE2. The structural organization of the RCNIV major IE region is therefore similar to that of human cytomegal ovirus (HCMV) and murine cytomegalovirus (MCMV). When we compared the predicted amino acid sequences of the IE1 proteins of RCMV, HCMV, and MCMV, no areas of homology were found across all three proteins, while a few small areas of homology were found between RCMV IE1 and MCMV IE 1. In contrast, large areas of homology were found across the carboxyl half of RCMV IE2, HCMV IE2, and MCMV ie3 proteins. In addition, simil arities were found at the beginning of exon 5 of RCMV and MCMV. The po ssible significance of these conserved regions is discussed. Dinucleot ide frequency analysis demonstrated a decrease in CpG frequency over t he IE region. The IE gene products were able to transactivate heterolo gous promoters.