Positive supercoiling facilitates RNAP elongation past protein-mediated DNA loops

Abstract

Some proteins, such as the lac repressor (LacI), induce the formation of loops that alter DNA topology and generate torsional barriers. The supercoiling generated by elongating RNA polymerase may facilitate passage through such barriers. Tethered particle motion measurements of E. coli RNA polymerase (RNAP) progress along templates in conditions that prevented, or favored, LacI-mediated DNA looping revealed that RNAP paused longer at unlooped LacI obstacles, or those barring entry to a loop, than those barring exit from the loop.