Positive control of endolysin synthesis in vitro by the gene N protein of phage lambda

Positive control in vitro by gene N protein of bacteriophage lambda was demonstrated. lambda DNA was used to direct in vitro synthesis of lambda endolysin in a cell-free protein-synthesizing preparation derived from Escherichia coli. The endolysin synthesis depends on the concomitant in vitro synthesis of lambda gene N protein. When lambda N(-) DNA was used to direct the cell-free preparation, endolysin was made only if extract was added from cells in which a lambda prophage had been induced. The use of various prophage deletion strains proved that if this stimulating activity made in vivo is coded by a known lambda gene, it must be coded by gene N. The ability to stimulate endolysin synthesis in vitro on a lambda N(-) DNA template, therefore, constitutes an assay for N protein.