Multiple hTAF(II)31-binding motifs in the intrinsically unfolded transcriptional activation domain of VP16.

Transcriptional activation domain (TAD) in virion protein 16 (VP16) of herpes simplex virus does not have any globular structure, yet exhibits a potent transcriptional activity. In order to probe the structural basis for the transcriptional activity of VP16 TAD, we have used NMR spectroscopy to investigate its detailed structural features. Results show that an unbound VP16 TAD is not merely "unstructured" but contains four short motifs (residues 424-433, 442-446, 465-467 and 472-479) with transient structural order. Pre-structured motifs in other intrinsically unfolded proteins (IUPs) were shown to be critically involved in target protein binding. The 472-479 motif was previously shown to bind to hTAF(II)31, whereas the hTAF(II)31-binding ability of other motifs found in this study has not been addressed. The VP16 TAD represents another IUP whose prestructured motifs mediate promiscuous binding to various target proteins.