DA-COMPLEX ASSEMBLY ACTIVITY REQUIRED FOR VP16C TRANSCRIPTIONAL ACTIVATION

One class of transcriptional activation domains stimulates the concert ed binding of TFIIA and TFIID to promoter DNA. To test whether this DA -complex assembly activity contributes significantly to the overall me chanism of activation in vivo, we analyzed mutants of the 38-amino-aci d residue VP16C activation subdomain from herpes simplex virus. An exc ellent correlation was observed between the in vivo activation functio n of these mutants and their in vitro DA-complex assembly activity. Mu tants severely defective for in vivo activation also showed reduced in vitro binding to native TFIIA. No significant correlation between in vivo activation function and in vitro binding to human TATA binding pr otein, human TFIIB, or Drosophila melanogaster TAF(II)40 was observed for this set of VP16C mutants. These results argue that the ability of VP16C to increase the rate and extent of DA-complex assembly makes a significant contribution to the overall mechanism of transcriptional a ctivation in vivo.