CCAAT BOX-DEPENDENT ACTIVATION OF THE TATA-LESS HUMAN DNA-POLYMERASE-ALPHA PROMOTER BY THE HUMAN CYTOMEGALOVIRUS 72-KILODALTON MAJOR IMMEDIATE-EARLY PROTEIN

Human cytomegalovirus (HCMV) immediate-early (IE) proteins are known p otent transregulators of viral and cellular gene expression upon HCMV infection. HCMV is known to activate a number of cellular genes intima tely associated with the cell cycle and DNA replication by mechanisms involving the viral major IE 86-kDa protein (IE2). We have recently sh own that IE2 mediates this activation in a TATA-dependent manner and i nteracts directly with the TATA-binding protein. However, a number of TATA-less cellular promoters, e.g., DNA polymerase or and dihydrofolat e reductase, are also activated by HCMV infection. Consequently, we ha ve asked how HCMV mediates this activation. We show that, consistent w ith its known TATA dependency, IE2 does not activate the DNA polymeras e or promoter. In contrast, this promoter is strongly activated by the major IE 72-kDa protein (IE1). Whilst deletion of ATF or E2F sites wi thin the DNA polymerase ex promoter had little effect on IE1-mediated activation, removal of the CCAAT box appeared to abolish high levels o f activation by IE1. Consistent with this observation, we also find th at IE1 interacts directly with the CCAAT box binding factor CTF1 in vi tro and massively augments CTF1-mediated activation of the DNA polymer ase or promoter in transient transfection assays.