NF-Y recruitment of TFIID, multiple interactions with histone fold TAFIIs

Abstract

The nuclear factor y (NF-Y) trimer and TFIID contain histone fold subunits, and their binding to the CCAAT and Initiator elements of the major histocompatibility complex class II Ea promoter is required for transcriptional activation. Using agarose-electrophoretic mobility shift assay we found that NF-Y increases the affinity of holo-TFIID for Ea in a CCAAT- and Inr-dependent manner. We began to dissect the interplay between NF-Y- and TBP-associated factors PO1II (TAFIIs)-containing histone fold domains in protein-protein interactions and transfections. hTAFII20, hTAFII28, and hTAFII18-hTAFII28 bind to the NF-Y B-NF-YC histone fold dimer; hTAFII80 and hTAFII31-hTAFII80 interact with the trimer but not with the NF-YB-NF-YC dimer. The histone fold α2 helix of hTAFII80 is not required for NF-Y association, as determined by interactions with the naturally occurring splice variant hTAFII80δ. Expression of hTAFII28 and hTAFII18 in mouse cells significantly and specifically reduced NF-Y activation in GAL4-based experiments, whereas hTAFII20 and hTAFII135 increased it. These results indicate that NF-Y (i) recruits purified holo-TFIID in vitro and (ii) can associate multiple TAFIIs, potentially accommodating different core promoter architectures.