Purification of H-NS protein and its regulatory effect on transcription in vitro

Abstract

This chapter discusses the purification of H-NS Protein and its regulatory effect o transcription in vitro . Subsets of Escherichia Coli DNA-binding proteins, which have been collectively termed histone-like proteins, are implicated in the compact organization of chromosomal DNA (i.e., the nucleoid structure). The best characterized are HU, H-NS, and IHF. Its coding gene, HNS, was sequenced and mapped at 27 min on the E. coli genetic map. H-NS is an abundant, neutral protein, composed of 137 amino acids, and appears to be homodimeric in a solution. Although this protein has been characterized as a relatively nonspecific DNA-binding protein, notable features are that it preferentially recognizes curved DNA sequences and induces strong condensation of DNA in vitro . H-NS can be categorized as a transcriptional regulator, which affects, either directly or indirectly, the expression of a number of unlinked genes in E. coli or Salmonella typhimurium . In an in vitro transcription assay, the H-NS protein was demonstrated previously to function as a transcriptional repressor directly and selectively for certain promoters.