One characteristic of human cytomegalovirus (HCMV) is the high complexity of its genome: the double-stranded DNA of approx 240 kbp contains the coding capacity for more than 200 different proteins (1,2). The genes encoding those proteins are expressed coordinately during the replication of this virus (3). Although posttranscriptional regulation has been described for HCMV, transcriptional regulation by promoter activation is believed to play a key role in mediating the cascade fashion of gene expression observed during the replicative cycle (4,5). Both viral and cellular proteins contribute to promoter activation. For instance, during the immediate-early (IE-) phase of gene expression, a strong enhancer-promoter drives transcription from the major IE gene region (6,7). This enhancer-promoter can both be regulated by cellular proteins such as transcription factors of the ATF/CREB and NF-κ-B family and viral proteins such as the tegument constituents pp71 and ppUL69 or the immediate early protein IE2-p86 (8-12).