Cellular Proteins Bind to Sequence Motifs in the R1 Element between the HCMV Immune Evasion Genes

The viral US3 and US6 gene products of human cytomegalovirus (CMV) are sequentially expressed at immediate-early and early times after infection, respectively. They downregulate the surface expression of HLA class I molecules. There are two repeat-containing regulatory regions between the US3 promoter and the US6 transcription unit designated R1 and R2. R2 contains repetitions of the NF-κB responsive element and enhances the immediate-early expression of the US3 gene. R1 contains 19 repetitions of a 5′-TRTCG-3′ pentanucleotide arranged as everted repeats, inverted repeats, and variably spaced single pentanucleotides. In the context of the viral genome, R1 also enhances immediate-early US3 gene expression by an unknown mechanism (G. C. Bullock, et al., 2001, Virology 288, 164–174). We report a sequence motif within the R1 element that binds a human cell nuclear protein which is antigenically related to the Drosophila boundary element-associated factor (BEAF). The potential role of a 35-kDa cellular protein that binds to sequence motifs within the R1 element in regulating the expression of the CMV US3 immune evasion gene is discussed.