In order to study the function of human cytomegalovirus (HCMV) immediate early gene 2 () (UL122) gene products made at late times during infection, cDNA clones were isolated from an expression library made with 74 h post-infection mRNA. Based on screening of the library, 1% of transcripts in infected cells at this time were region-specific, and transcripts encoding γIE2, a 40K late gene product, were more abundant than those encoding IE2, an α gene product made throughout infection. As expected, the cDNA capable of directing the expression of γIE2 was derived from a contiguous genomic region within exon 5 of the region. The cDNA clones encoding γIE2 and IE2 were compared for their ability to trans-activate viral and cellular promoters and to repress expression from the promoter via the cis-repression signal. Unexpectedly, γIE2 trans-activated a variety of test promoters when cotransfected with the major α gene product, IE1. Promoters derived from the cellular β-actin gene, the simian virus 40 early region and the human immunodeficiency virus were all responsive to γIE2 plus IE1, although several β promoters derived from the HCMV genome were unresponsive. Thus, this abundant late product from the region may play a role in trans-activation in addition to its role as a repressor of α gene expression.


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