Acf1, the largest subunit of CHRAC, regulates ISWI-induced nucleosome remodelling

AUTOR(ES)

Eberharter, Anton

FONTE

Oxford University Press

RESUMO

The chromatin accessibility complex (CHRAC) was originally defined biochemically as an ATP-dependent ‘nucleosome remodelling’ activity. Central to its activity is the ATPase ISWI, which catalyses the transfer of histone octamers between DNA segments in cis. In addition to ISWI, four other potential subunits were observed consistently in active CHRAC fractions. We have now identified the p175 subunit of CHRAC as Acf1, a protein known to associate with ISWI in the ACF complex. Interaction of Acf1 with ISWI enhances the efficiency of nucleosome sliding by an order of magnitude. Remarkably, it also modulates the nucleosome remodelling activity of ISWI qualitatively by altering the directionality of nucleosome movements and the histone ‘tail’ requirements of the reaction. The Acf1–ISWI heteromer tightly interacts with the two recently identified small histone fold proteins CHRAC-14 and CHRAC-16. Whether topoisomerase II is an integral subunit has been controversial. Refined analyses now suggest that topoisomerase II should not be considered a stable subunit of CHRAC. Accordingly, CHRAC can be molecularly defined as a complex consisting of ISWI, Acf1, CHRAC-14 and CHRAC-16.

Documentos Relacionados

• HuCHRAC, a human ISWI chromatin remodelling complex contains hACF1 and two novel histone-fold proteins
• The DNA chaperone HMGB1 facilitates ACF/CHRAC-dependent nucleosome sliding
• ACF1 improves the effectiveness of nucleosome mobilization by ISWI through PHD–histone contacts
• Acf1 confers unique activities to ACF/CHRAC and promotes the formation rather than disruption of chromatin in vivo
• dMi-2 and ISWI chromatin remodelling factors have distinct nucleosome binding and mobilization properties