Coordination of PIC assembly and chromatin remodeling during differentiation-induced gene activation.

We analyzed the ordered recruitment of factors to the human alpha1 antitrypsin promoter around the initial activation of the gene during enterocyte differentiation. We found that a complete preinitiation complex, including phosphorylated RNA pol II, was assembled at the promoter long before transcriptional activation. The histone acetyltransferases CBP and P/CAF were recruited subsequently, but local histone hyperacetylation was delayed. After transient recruitment of the human Brahma homolog hBrm, remodeling of the neighboring nucleosome coincided with transcription initiation. The results suggest that, at this promoter, chromatin reconfiguration is a defining step of the initiation process, acting after the assembly of the Pol II machinery.