Chromatin remodeling: insights and intrigue from single-molecule studies

Chromatin remodelers are ATP-hydrolyzing machines specialized to restructure, mobilize or eject nucleosomes, allowing regulated exposure of DNA in chromatin. Recently, remodelers have been analyzed using single-molecule techniques in real time, revealing them to be complex DNA-pumping machines. The results both support and challenge aspects of current models of remodeling, supporting the idea that the remodeler translocates or pumps DNA loops into and around the nucleosome, while also challenging earlier concepts about loop formation, the character of the loop and how it propagates. Several complex behaviors were observed, such as reverse translocation and long translocation bursts of the remodeler, without appreciable DNA twist. This review presents and discusses revised models for nucleosome sliding and ejection that integrate this new information with the earlier biochemical studies.