Studying on the 19-bp Palindrome Repeats in Human Cytomegalovirus Immediate Early Enhancer/Promoter Reveals their Diversity in Function for the Promoter Activity

The human cytomegalovirus major immediate early enhancer/promoter (HCMV MIEP), extending from -588 to +1 relative to the transcription start site, contains a series of reiterated cis-acting elements, such as 19-bp repeats, which occur four times in the enhancer/promoter region. However, it is still not clear whether these elements repeat just for backing up or they really execute various indispensable functions. We show here that these reiterated elements are functionally different from each other through serial deletion mutation and site-directed mutation. In addition, we also found that the CG-reverse in the first 19-bp repeat could improve the transcription activity of MIEP in HeLa cells and impair the protein-binding capacity in the EMSA assay. The expression feature of this mutated MIEP in transgenic mice further confirmed its stronger and more universal transcription activity in vivo.