The ATP-Dependent Remodeler RSC Transfers Histone Dimers and Octamers through the Rapid Formation of an Unstable Encounter Intermediate

摘要

RSC, an essential chromatin remodeling complex in budding yeast, is involved in a variety ofnbiological processes including transcription, recombination, repair, and replication.How RSC participates innsuch diverse processes is not fully understood. In vitro, RSC uses ATP to carry out several seemingly distinctnreactions: it repositions nucleosomes, transfersH2A/H2B dimers between nucleosomes, and transfers histonenoctamers between pieces of DNA. This raises the intriguing mechanistic question of how this molecularnmachine can use a single ATPase subunit to create these varied products. Here, we use a FRET-basednapproach to kinetically order the products of the RSC reaction. Surprisingly, transfer of H2A/H2B dimersnand histone octamers is initiated on a time scale of seconds when assayed by FRET, but formation of stablennucleosomal products occurs on a time scale of minutes when assayed by native gel. These results suggest anmodel in which RSC action rapidly generates an unstable encounter intermediate that contains the twonexchange substrates in close proximity. This intermediate then collapses more slowly to form the stablentransfer products seen on native gels. The rapid, biologically relevant time scale onwhich the transfer productsnare generated implies that such products can play key roles in vivo.