This mutated E2F1 was still able to synergistically activate transcription with Sp1 and could interact with Sp1 in the presence of nuclear extract, suggesting that there is a cellular factor that can mediate the interaction of E2F and Sp1. In addition to histones, the possibility that Sp1 may be an acetylation substrate is being tested. Phosphate incorporation into Sp1 also correlates with maximal interaction of E2F1 and Sp1. Of these mutations, only the Ser654 showed a significant reduction in phosphorylation. There also appear to be additional phosphorylation sites in the C-terminal D domain.
Experiments are underway to further characterize the kinase.
Effects of HCMV on Host Cell Cycle. Infection of cells with several different DNA viruses results in a controlled program of viral gene expression executed through cellular transcription factors. The host cell generally undergoes a proliferative response accompanied by changes in expression of many host cell genes, some of which are likely to be essential for productive viral infection. Cytomegalovirus is a herpes virus that is usually asymptomatic but when acquired by an immunocompromised host, such as an HIV patient or a pregnant woman, has profound consequences. We have been studying the effect of HCMV infection on the E2F family of transcription factors, based on our initial finding that HCMV IE1 gene product activates E2F-dependent transcription and interacts with E2F1 and thereby activates transcription of DHFR and a number of cellular genes associated with a proliferative response.