The RSC Chromatin Remodeling ATPase can Translocate DNA with High Force and Small Step Size

Abstract

ATP-dependent chromatin remodeling complexes (remodelers) use the energy of ATP hydrolysis to reposition and reconfigure nucleosomes. Despite their diverse functions, all remodelers share highly conserved catalytic ATPase domains, many of which are shown to translocate DNA. Understanding remodeling requires biophysical knowledge of the DNA translocation process: how the ATPase moves DNA and generates force, and how translocation and force generation are coupled on nucleosomes. Here we characterize the real-time activity of a minimal translocase ‘motor’ complex isolated from a prototypical remodeler (RSC) on bare DNA, using high-resolution optical tweezers and a ‘tethered’ translocase system. We observe on dsDNA a processivity of ∼35 bp, a speed of ∼25 bp/sec, and a step size of 1.9 (± 0.3, s.d.) bp. Surprisingly, the motor is capable of moving against high force, up to 30 pN, making it one of the most force-resistant motors known. We also provide evidence for DNA ‘buckling’ at initiation. These observations extend and clarify measurements of nucleosome-dependent translocation by the complete RSC or SWI/SNF complex, and reveal the ATPase as a powerful and versatile DNA translocating motor capable of disrupting DNA-histone interactions by mechanical force using a small step size.