Host-Controlled Modification of DNA

Abstract

The study of host-specific modification and restriction of DNA has its root in a series of independent observations, made some 15 years ago by several groups of authors who worked with various bacteriophages (see Arber, 1965). Let us recall the results of the experiments made by Bertani and Weigle (1953) with bacteriophage A. This phage is usually grown on strains of E. coli K12, and we call it then λ.K. Phage λ.K also grows with full efficiency of plating on E. coli strain C, but if one tries to infect again strain K12 with λ.C, only a low proportion, or some 4 × 10^-4 of the phage give rise to the production of a progeny; the others are said to be restricted by K12. Phage isolated from the rare plaques grown on K12 show to be modified λ.K since they grow again with full efficiency on K12. They cannot be explained as being host range mutants, since the ability to grow on K12 is not maintained upon consecutive multiplication of the phage on strain C.