Abstract
From DNA-RNA hybrid studies, it was concluded that about 8 per cent of the [lambda] genome is complementary to the DNA of E. coli strains W3110 and B/5. At least 80 per cent of this homology lies outside of the [lambda] b2+ segment of the genome. There is no homology between [lambda] and Shigella dysenteriae, as defined experimentally. Various lines of evidence support the view that the observed homology is required for the formation of the lysogenic state rather than for trans-duction.