Regulation of the Expression of the N Gene of Bacteriophage Lambda

A quantitative assay for the N protein of bacteriophage lambda has been used to study the in vivo regulation of N gene expression. The assay makes use of the observation that in a cell-free protein-synthesizing system from Escherichia coli programmed with lambdaN(-) DNA the lambda endolysin is made only if N protein is added to the reaction. The rate of synthesis of N protein in vivo is negatively controlled by the products of the CI and tof genes of the phage. Furthermore, N protein activity is extremely unstable in vivo. During normal cell growth at 35 degrees , the half-life of N protein is about 2 min.