Kappa, a novel factor for the arrest of transcription in vitro by DNA-dependent RNA polymerase from Escherichia coli at specific sites of natural templates.

Abstract

A procedure for the isolation of a novel factor, named x, effecting termination or block of transcription of DNAs of bacteriophages T4, T5 and T7 by Escherichia coli RNA polymerase is described.This protein is a dimer of two apparently identical peptide chains, the latter with a molecular weight of about 17000. x is bound to double‐stranded DNA in almost tight packing. It does not influence initiation of transcription. The net rate of RNA synthesis is reduced. The kinetics of transcription in vitro of phage DNAs in the presence of a saturating amount of x lead to a plateau over a wide range of ionic strength. The average chain length of the product at this plateau is 40–50% of that of the product obtained without the factor.The RNA remains bound to the DNA in the blocked end state.Hybridization‐saturation and competition and sedimentation on analysis sucrose gradients yield evidence that the blocking action occurs at a few specific sites of the many x‐binding sites on the DNA.The possible role of this factor is discussed.