SNAP(c): a core promoter factor with a built-in DNA-binding damper that isdeactivated by the Oct-1 POU domain

snRNA gene transcription is activated in part by recruitment of SNAP(c) to the core promoter through protein-protein contacts with the POU domain of t he enhancer-binding factor Oct-1. We show that a mini-SNAP(c) consisting of a subset of SNAP(c) subunits is capable of directing both RNA polymerase I I (Pol II) and Pol III snRNA gene transcription. Mini-SNAP(c) cannot be rec ruited by Oct-1, but binds as efficiently to the promoter as SNAP(c) togeth er with Oct-1 and directs activated RNA Pal III transcription. Thus, SNAP(c ) represses its own binding to DNA, and repression is relieved by interacti ons with the Oct-1 POU domain that promote cooperative binding. We have sho wn previously that TBP also represses its own binding, and in that case rep ression is relieved by cooperative interactions with SNAP(c). This may repr esent a general mechanism to ensure that core promoter-binding factors, whi ch have strikingly slow off-rates, are recruited specifically to promoter s equences rather than to cryptic-binding sites in the genome.