Interconvertible lac repressor-DNA loops revealed by single-molecule experiments.

ABSTRACT: At many promoters, transcription is regulated by simultaneous binding of a protein to multiple sites on DNA, but the structures and dynamics of such transcription factor-mediated DNA loops are poorly understood. We directly examined in vitro loop formation mediated by Escherichia coli lactose repressor using single-molecule structural and kinetics methods. Small ( approximately 150 bp) loops form quickly and stably, even with out-of-phase operator spacings. Unexpectedly, repeated spontaneous transitions between two distinct loop structures were observed in individual protein-DNA complexes. The results imply a dynamic equilibrium between a novel loop structure with the repressor in its crystallographic "V" conformation and a second structure with a more extended linear repressor conformatio

SUBMITTER: Wong OK 

PROVIDER: S-EPMC2553838 | biostudies-literature | 2008 Sep

REPOSITORIES: biostudies-literature