Sandford G R, Ho K, Burns W H
Johns Hopkins Oncology Center, Baltimore, Maryland 21231.
J Virol. 1993 Jul;67(7):4093-103. doi: 10.1128/JVI.67.7.4093-4103.1993.
A major locus of rat cytomegalovirus (RCMV) immediate-early (IE) RNA transcription was identified. A cDNA library from rat embryo fibroblasts 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. The 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 RCMV major IE region is therefore similar to that of human cytomegalovirus (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 IE1. In contrast, large areas of homology were found across the carboxyl half of RCMV IE2, HCMV IE2, and MCMV ie3 proteins. In addition, similarities were found at the beginning of exon 5 of RCMV and MCMV. The possible significance of these conserved regions is discussed. Dinucleotide frequency analysis demonstrated a decrease in CpG frequency over the IE region. The IE gene products were able to transactivate heterologous promoters.
鉴定出大鼠巨细胞病毒（RCMV）立即早期（IE）RNA转录的一个主要位点。构建了在IE条件下感染RCMV的大鼠胚胎成纤维细胞的cDNA文库，并使用合适的RCMV DNA探针进行筛选，结果显示该位点通过差异剪接转录出至少两个IE基因（IE1和IE2）。前三个外显子（第一个为非编码外显子）与外显子4剪接形成IE1，与外显子5剪接形成IE2。因此，RCMV主要IE区域的结构组织与人类巨细胞病毒（HCMV）和小鼠巨细胞病毒（MCMV）的相似。当我们比较RCMV、HCMV和MCMV的IE1蛋白的预测氨基酸序列时，在这三种蛋白中未发现同源区域，而在RCMV IE1和MCMV IE1之间发现了一些小的同源区域。相比之下，在RCMV IE2、HCMV IE2和MCMV ie3蛋白的羧基端一半区域发现了大片同源区域。此外，在RCMV和MCMV外显子5的起始处发现了相似性。讨论了这些保守区域的可能意义。二核苷酸频率分析表明，IE区域的CpG频率降低。IE基因产物能够反式激活异源启动子。
