Biology Department Seminar

Nucleosome disassembly in the promoter region is a vital process in the transcription initiation of eukaryotes. Histone chaperone CIA/ASF1, which is the most conserved histone chaperone in eukaryotes, is involved in this process. Since histone acetylation is a well-known signal for transcription activation, the interaction between CIA/ASF1 and the CCG1 double-bromodomain (DBDCCG1) in the TFIID complex, which recognizes acetylated histones, (1) seems to play a critical role in the nucleosome disassembly in promoter regions with histone acetylation. In order to elucidate the mechanism of the site-specific nucleosome disassembly, we determined the crystal structures of the CIA/ASF-histone-H3-H4 (2) and CIA/ASF1-DBDCCG1 complexes. The crystal structure of the CIA/ASF1-histone-H3-H4 complex and a biochemical analysis demonstrated that CIA/ASF1 splits the histone (H3-H4)2 tetramer into two histone H3-H4 dimers (2). The crystallographic, biochemical, and biological analyses of the CIA/ASF1-DBDCCG1 complex suggested that DBDCCG1 in the TFIID complex recruits CIA/ASF1 to promoter region(s), leading to histone eviction through the interaction between CIA/ASF1 and histone-H3-H4 (3). The CIA/ASF1 recruitment also facilitates the RNA polymerase II entry to the promoter region(s). The general transcription initiation factor TFIID seems to play a vital role in the histone eviction around the promoter region through interaction with the histone chaperone CIA/ASF1.
References: (1) Chimura et al. (2002) PNAS 99, 9334-9339. (2) Natsume, R. et al. (2007) Nature 446, 338-341. (3) Akai, Y. et al. submitted.