Purification and characterization of the N gene product of bacteriophage lambda

Abstract The N protein (p N ) specified by bacteriophage λ is an antitermination factor and is required for phage development. p N can be assayed by making use of the observation that the in vitro synthesis of trp mRNA in a reaction programmed with DNA template from λ trp transducing phage bearing N $ and fed $ mutations is p N dependent (Ishii et al., 1980). The assay has been used to purify p N . We have observed that p N forms a complex with E. coll protein(s) and is dissociated in the presence of urea. The complex is not formed in host bacteria bearing the nusA _ nusB _ mutations. p N is a basic protein and heat-stable. Using these characteristics, we have purified p N to virtual homogeneity as judged by polyacrylamide gel electrophoresis in the presence of SDS. p N is a monomeric protein and its mol. wt. is approx. 14 000. The antiterminating activity of p N appears to be enhanced by complex formation with host-encoded protein(s) depending on the nusA and/or nusB gene function.