Identification of Additional IE2-p86-Responsive cis-Repressive Sequences within the Human Cytomegalovirus Major Immediate Early Gene Promoter

Abstract

Human cytomegalovirus (HCMV) is a ubiquitous human pathogen that is the leading viral cause of birth defects and also causes significant morbidity and mortality in immunosuppressed individuals. The immediate early (IE) genes, IE1-p72 and IE2-p86, are the first HCMV genes expressed after infection under the control of a strong transcriptional enhancer-promoter, the major IE promoter (MIEP). Gene expression mediated by the predominant IE2-p86 is believed to be essential for the progression of viral production, as well as for the development of HCMV-associated pathogenesis. To gain further understanding of the transcriptional activity of IE2-p86, we attempted to isolate its downstream target genes within the HCMV genome. By a modified approach coupling the methods of cyclic amplification and selection of targets and selection and amplification of binding sites, several HCMV genomic fragments were identified based on their ability to bind to IE2-p86. Two additional IE2-p86-responsive elements other than the cis-repressive sequence (CRS) were identified within the MIEP and were termed –240 and –170 boxes. These two cis elements resemble the CRS in their sequences, as they contain the CG(N)₁₀CG motif. The binding of IE2-p86 to these two distal CRS-like sequences was further confirmed by DNase I footprinting analysis and electrophoretic mobility shift assay. Promoter activity analysis in the transient expression system suggested that these two cis elements act functionally as IE2-p86-responsive repressive sequences to cooperate with the CRS to suppress MIEP expression.