Regulation by N gene protein of phage lambda of anthranilate synthetase synthesis in vitro

The N protein of bacteriophage lambda is a positive regulator of early lambda gene expression. In a lambdatrp transducing phage, lambdatrp46Nam, the synthesis of trp enzymes in vivo is also dependent on the presence of active N protein. The DNA of this phage has been used in a protein-synthesizing system in vitro to develop a biochemical assay for the activity of the N protein. From the following observations it appears that it is the N protein itself that stimulates trp enzyme synthesis in vitro. An activity that stimulates trp enzyme synthesis can be made in vitro by lambdaN(+) DNA but not by lambdaNam DNA. This activity can also be detected in extracts of induced lambdaN(+) lysogens but not of lambdaNam lysogens. Furthermore, the activity is temperature sensitive in similar extracts of lambdaNts lysogens. No such activity is detectable in extracts of induced lysogens of lambdaimm(21). This phage makes all lambda-coded gene products outside the immunity region, but lacks an N protein activity able to substitute for N(lambda) protein in vivo. Our experiments also show that the action of N protein is inhibited by the cI repressor protein in vivo as it is in vivo.