DNA translocation and loop formation mechanism of chromatin remodeling by SWI/SNF and RSC.

ATP-dependent chromatin-remodeling complexes (remodelers) modulate gene transcription by regulating the accessibility of highly packaged genomic DNA. However, the molecular mechanisms involved at the nucleosomal level in this process remain controversial. Here, we monitor the real-time activity of single ySWI/SNF or RSC complexes on single, stretched nucleosomal templates under tensions above 1 pN forces. We find that these remodelers can translocate along DNA at rates of approximately 13 bp/s and generate forces up to approximately 12 pN, producing DNA loops of a broad range of sizes (20-1200 bp, average approximately 100 bp) in a nucleosome-dependent manner. This nucleosome-specific activity differs significantly from that on bare DNA observed under low tensions and suggests a nucleosome-remodeling mechanism through intranucleosomal DNA loop formation. Such loop formation may provide a molecular basis for the biological functions of remodelers.