The Oct-1 POU domain activates snRNA gene transcription by contacting a region the SNAP(c) largest subunit that bears sequence similarities to the Oct-1 coactivator OBF-1

The RNA polymerases II and III snRNA gene promoters contain an octamer sequ ence as part of the enhancer and a proximal sequence element (PSE) as part of the core promoter. The octamer and the PSE bind the POU domain activator Oct-1 and the basal transcription factor SNAP(c), respectively. Oct-1, but not Oct-1 with a single E7R mutation within the POU domain, binds cooperat ively with SNAP, and, in effect, recruits SNAP, to the PSE. Here, we show t hat SNAP, recruitment is mediated by an interaction between the Oct-1 POU d omain and a small region of the largest subunit of SNAP, SNAP190. This SNAP 190 region is strikingly similar to a region in the B-cell-specific Oct-1 c oactivator, OBF-1, that is required for interaction with octamer-bound Oct- 1 POU domain. The Oct-1 POU domain-SNAP190 interaction is a direct protein- protein contact as determined by the isolation of a switched specificity SN AP190 mutant that interacts with Oct-1 POU E7R but not with wild-type Oct-1 POU. We also show that this direct protein-protein contact results in acti vation of transcription. Thus, we have identified an activation target of a human activator, Oct-1, within its cognate basal transcription complex.