Characterization of Cnu protein binding to oriC in escherichia coli

Abstract

Chromosomal DNA replication in Escherichia coli starts from a single point called oriC which contains several DNA binding sites for several proteins such as IciA, DnaA and FIS in the DNA replication complex. By measuring survival frequency, a novel protein was identified as an oriC binding protein, Cnu (oriC-binding nucleoid-associated). Cnu is composed of 71 amino acids. Cnu has an extensive amino acid identity with Hha protein, an H-NS associate. Cnu was regarded as a specific H-NS binding protein based on in vivo analysis with knock-out mutants and in vitro cross-linking assay. Genetic studies with cnu and has mutants suggested that Cnu binds to oriC only if Cnu complexes with H-NS. To characterize Cnu in DNA replication, the in vitro binding assay was studied. From gel retardation assay, Cnu itself does not bind to oriC but affects on the H-NS binding. This result supports the idea that the formation of Cnu:H-NS complex might be a key player in DNA replication.