KAP-1, A NOVEL COREPRESSOR FOR THE HIGHLY CONSERVED KRAB REPRESSION DOMAIN

The KRAB repression domain is one of the most widely distributed trans criptional effector domains yet identified, but its mechanism of repre ssion is unknown. We have cloned a corepressor, KAP-1, which associate s with the KRAB domain but not with KRAB mutants that have lost repres sion activity. KAP-1 can enhance KRAB-mediated repression and is a rep ressor when directly tethered to DNA. KAP-1 contains a RING finger, B boxes, and a PHD finger; the RING-B1-B2 structure is required for KRAB binding and corepression. We propose that KAP-1 may be a universal co repressor for the large family of KRAB domain-containing transcription factors.