STRUCTURAL FLEXIBILITY IN TRANSCRIPTION COMPLEX-FORMATION REVEALED BYPROTEIN-DNA PHOTO-CROSS-LINKING

The Oct-1 POU domain binds diverse DNA-sequence elements and forms a h igher-order regulatory complex with the herpes simplex virus coregulat or VP16. The POU domain contains two separate DNA-binding domains join ed by a flexible linker. By protein-DNA photocrosslinking we show that the relative positioning of the two POU DNA-binding domains on DNA va ries depending on the nature of the DNA target, On a single VP16-respo nsive element, the POU domain adopts multiple conformations. To determ ine the structure of the Oct-1 POU domain in a multiprotein complex wi th VP16, we allowed VP16 to interact with previously crosslinked POU-d omain-DNA complexes and found that VP16 can associate with multiple PO U-domain conformations. These results reveal the dynamic potential of a DNA-binding domain in directing transcriptional regulatory complex f ormation.