Control and Selectivity of   DNA Transcription in Lysogenic Bacteria

The maintenance of ~ as a stable prophage within the chromosome of its lysogenic host requires the integrity of a specific region of the prophage called C I (Campbell, 1962), whose r l is to repress, by means of a diffusible product, genes essential for the early vegetative development of the virus (Jacob and Monod, 1961). E coli cells lysogenic for a ~ prophage thus constitute a particularly suitable system for investigating in vivo (and possibly, in vitro) the features of repression at the DNA level. Not only does the early phage region under repressor command presumably comprise, unlike repressed bacterial operons, quite an appreciable portion of the total genome, but the "early " genes involved in phage