Regulation of human cytomegalovirus immediate-early gene expression

The positive and negative cis-acting elements that affect transcription from the human cytomegalovirus major immediate-early (MIE) promoter and the viral and cellular proteins that bind to these elements are discussed. The data obtained using in vitro transcription and transient transfection assays are reviewed and compared to recent data using recombinant viruses with cis-acting elements deleted. The effects of cell type and cellular differentiation on activation of transcription from the MIE promoter are compared with the effects of mitogens and virion-associated tegument proteins that directly or indirectly activate protein kinase pathways. The repressor and enhancer regions upstream of the MIE promoter in the large unique component of the viral genome are compared to the elements upstream of the more simplified IEUS3 promoter in the short unique component of the viral genome.