The nusA gene protein of Escherichia coli: Its identification and a demonstration that it interacts with the gene N transcription anti-termination protein of bacteriophage lambda

Abstract

In an infection of Escherichia coli K12 the N gene protein of bacteriophage λ is needed to prevent premature termination of transcription at termination sites located within the P L and P R operons of the phage. A protein coded by the E. coli nusA gene is also required because N protein fails to prevent transcription termination in a nusA mutant of E. coli. Starting with a crude 35S-labelled E. coli lysate we have identified two proteins, of apparent molecular weights 69,000 and 25,000, during electrophoresis in the presence of sodium dodecyl sulphate, which bind tightly and specifically to an affinity column containing pure N protein covalently bound to Sepharose. The 69,000 M r protein is unusually acidic (p I ~ 4·7). We were able to identify it as the product of the nusA gene because it is temperature-sensitive in vitro and has a changed isoelectric point when it is derived from a strain with the temperature-sensitive mutation nusA1. The 25,000 M r N-binding protein has not yet been identified. groN785, an E. coli multiple mutant which is non-permissive for λ N gene function, also has a nusA gene protein with an altered isoelectric point. Although groN785 has an RNA polymerase mutation and at least one other mutation that are both necessary for its phenotype, the nusA gene mutation in groN785 is not necessary for the resistance of the strain to bacteriophage λ. Implications of these observations for the mechanism of transcription termination control are discussed.