TAF-like functions of the human cytomegalovirus immediate-early proteins in promiscuous activation and cell cycle effects

We have analyzed mechanisms used by the HCMV IE proteins to activate transcription. We have shown that the IEPs act as promiscuous co-activators of transcription. IEP86 shows preferences in activating simple promoters by associating with multiple upstream bound factors. IEP72 synergizes with IEP86 without directly interacting with these factors. These mechanisms are conserved in the activation of complex viral and cellular promoters by the IEPs. The IEPs bridge to the basal complex by multiple interactions with TFIID, in a TAF-like fashion. IEP72 and IEP86 expressed during viral infection co-purify with TFIID over phosphocellulose, and co-immunoprecipitate with TFIID. IEP72 and IEP86 contact hTAF$\rm\sb{II}$130 simultaneously, and simultaneous contact is required to fully rescue the ts transcriptional defect in TAF$\rm\sb{II}$250 in the BHK-21 cell line, ts13. The IEPs do not rescue the defect in cell cycle progression in these cells. This effect is correlated with the inability of the IEPs to down-regulate the promoter of the cell cycle inhibitor p21/WAF1/CIP1. Regardless of the inability to rescue the cell cycle defect, IEP expression in ts13 cells at the non-permissive temperature rescues the cells from apoptosis, and this effect is independent of transcriptional activation. The promiscuous activity of the IEPs is thus due to their ability to co-activate transcription in a TAF-like fashion. We have taken the approach of studying protein-protein interactions between the IEPs and cellular proteins in order to understand the observed activities of the IEPs. The thesis has been guided by our lab\u27s previous investigations into the functions of SV40 large T antigen, and we have found that the IEPs are qualitatively very similar in mechanism to large T. However, the IEPs have not been independently correlated with transformation in any model system, so the comparison of the IEPs with T antigen also provides an opportunity to contrast the similarities between the mechanisms of the proteins with differences in their effects on host cell metabolism