here’s been lots of buzz about nucleosomes and RNAs lately. In fact, just last week EpiGenie reported that transcription initiation RNAs (tiRNAs) might be formed as RNA Pol II hits a nucleosome and backtracks. Nucleosomal post-transcriptional mods can cause RNA Polymerase II to pause or abort, while others can kick transcription into high gear.
But Pol II’s relationship with nucleosomes remains a bit of a mystery. Why Pol II stalls, or backtracks, or proceeds is one thing. How Pol II gets past them is yet another.
Using a dual-trap optical tweezers system, researchers at UC-Berkeley and the NCI watched and measured as the polymerase tried to read a strand of DNA. They found that the enzyme doesn’t actively unravel DNA from the nucleosome. Rather, it waits for a stochastic hiccup to relieve the tension between the nucleosome and the DNA strand that’s wound around it, and then jumps at the opportunity to sneak past — transcribing as it goes and transferring the histones upstream.
See how this might be another way of controlling RNA production, in tomorrow’s issue of Science, July 31, 2009