SNAPc: a core promoter factor with a built-in DNA-binding damper that is deactivated by the Oct-1 POU domain

摘要

snRNA gene transcription is activated in part by recruitment of SNAPc to the core promoter through protein–protein contacts with the POU domain of the enhancer-binding factor Oct-1. We show that a mini-SNAPc consisting of a subset of SNAPc subunits is capable of directing both RNA polymerase II (Pol II) and Pol III snRNA gene transcription. Mini-SNAPc cannot be recruited by Oct-1, but binds as efficiently to the promoter as SNAPc together with Oct-1 and directs activated RNA Pol III transcription. Thus, SNAPc represses its own binding to DNA, and repression is relieved by interactions with the Oct-1 POU domain that promote cooperative binding. We have shown previously that TBP also represses its own binding, and in that case repression is relieved by cooperative interactions with SNAPc. This may represent a general mechanism to ensure that core promoter-binding factors, which have strikingly slow off-rates, are recruited specifically to promoter sequences rather than to cryptic-binding sites in the genome.