Synergistic action of RNA polymerases in overcoming the nucleosomal barrier

During gene expression, RNA polymerase (RNAP) encounters a major barrier at a nucleosome and yet must access the nucleosomal DNA. In vivo evidence suggests that multiple RNAPs might increase transcription efficiency through nucleosomes. Here we have quantitatively investigated this hypothesis using E. coli RNAP as a model system by directly monitoring its location on the DNA via a single molecule DNA unzipping technique. When an RNAP encountered a nucleosome, it paused with a distinctive 10-bp periodicity and was backtracked by ~10–15 bp. When two RNAPs elongated in close proximity, the trailing RNAP assisted the leading RNAP elongation, reducing its backtracking and enhancing its transcription through a nucleosome by a factor of 5. Taken together, our data indicate that histone-DNA interactions dictate RNAP pausing behavior, and alleviation of nucleosome-induced backtracking by multiple polymerases may serve as a mechanism for overcoming the nucleosomal barrier in vivo.