A Single Molecule Study of Gene Silencing by HNS Protein DNA Interactions

Abstract

Histone-like nucleoid structuring (H-NS) proteins are an important prokaryotic protein responsible for organizing and compacting chromosomal DNA. Recently, it was found that H-NS can identify foreign genes acquired by horizontal gene transfer (HGT), based on AT content, and selectively silence these genes. Single-molecule studies have shown that H-NS binding can affect DNA rigidity and sometimes loop the DNA. However, most of these studies are done with λ DNA, which is neither part of the bacterial genome nor a sequence commonly acquired by HGT. We have been using optical tweezers to study gene silencing by H-NS on a variety of Salmonella genes whose interaction with H-NS is well characterized in vivo. We have also been studying how the presence of various cofactors of H-NS, such as Hha, cooperatively affect these genes. These experiments greatly improve our understanding of the biophysical mechanism behind how H-NS protein selectively interacts with and silences foreign DNA.