Properties of the N gene transcription antitermination protein of bacteriophage lambda

The product of the N gene of bacteriophage lambda prevents the termination of lambda early transcription. Here we describe the physical properties of pure lambda N protein. N protein is small and very basic. The apparent Mr of N protein during electrophoresis in the presence of sodium dodecyl sulfate is 12,500. It contains 22 mol % (arginine plus lysine) and only one methionine. The methionine residue is at the blocked NH2 terminal since N protein is not detectably shortened by reaction with cyanogen bromide. When use is made of the DNA sequence of the N gene region of lambda DNA (Franklin, N. C., and Bennett, G. N. (1979) Gene 8, 107-119), the lack of an internal methionine residue, the size, and the amino acid composition of N protein can be used to predict that N protein contains 107 amino acids (calculated Mr = 12,241) and that its coding sequence begins at position 223 of the lambda pL operon mRNA. N protein can be assayed by its ability to stimulate endolysin synthesis in vitro in a reaction programmed with lambda N- DNA. N protein activity is heat-stable and trypsin-sensitive. Its sedimentation velocity in a sucrose gradient and its Stokes' radius indicate that N protein is an extremely asymmetric monomer (f/fmin = 1.6). The relationship between this high degree of molecular asymmetry and the sequence which N protein must recognize in lambda nucleic acid is discussed.