PC2, originally isolated from HeLa nuclear extracts as a protein complex with a molecular size around 500 kDa, corresponds to the smaller form of human Mediator complexes described earlier in the Mediator section. This protein complex can enhance transcription mediated by Gal4-AH and HNF4 in an in vz'iro-reconstituted transcription system with DNA templates (Malik et al., 2000). The coactivating activity of PC2 requires the presence of other general cofactors, since PC2 alone only weakly stimulates activator-dependent transcription and in conjunction with TAFs, PC3, and PC4, a synergistic activation of Gal4-VP16-mediated transcription recapitulating the stimulatory activity of the USA fraction is detected (Malik et al, 2000). Likewise, PC2 is able to function together with PC3 and PC4 to regulate transcription mediated by TRct (Fondell et al, 1999), NFkB, Spl (Guermah et al, 1998), and the B-cell-specific Oct-l-OCA-B transcription complex (Luo et al, 1998).

0 0

Post a comment