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In order to study the function of human cytomegalovirus (HCMV) immediate early gene 2 (ie2) (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 ie2 region-specific, and transcripts encoding γIE2338aa, a 40K late gene product, were more abundant than those encoding IE2 579aa, an a gene product made throughout infection. As expected, the cDNA capable of directing the expression of γIE2338aa was derived from a contiguous genomic region within exon 5 of the ie1/ie2 region. The cDNA clones encoding γIE2338aa and IE2579aa were compared for their ability to trans-activate viral and cellular promoters and to repress expression from the ie1/ie2 promoter via the ie2 cis-repression signal. Unexpectedly, γIE2338aa trans-activated a variety of test promoters when cotransfected with the major a gene product, IE1491aa. Promoters derived from the cellular β-actin gene, the simian virus 40 early region and the human immunodeficiency virus were all responsive to γIE2338aa plus IE1491aa, although several β promoters derived from the HCMV genome were unresponsive. Thus, this abundant late product from the ie2 region may play a role in trans-activation in addition to its role as a repressor of α gene expression.
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