[Phenotypic characteristics of a new modification-restriction system in E. coli]

It has been demonstrated phenotypically that there exists a new modificational-and-restrictional system as synthesized by the recombinant Escherichia coli tF strain. A series of passages of the T3 and T7 phages and their mutants in E. coli tF has made it possible to ascertain a specific modification of the phage DNA, with was shown to be induced by the host strain. The high level of adsorption of these phages on the cell surface of E. coli tF has ruled out the possibility of existing of a 'nonclassical' modification and restriction of DNA. In view of the further characterizing of this modificational-and-restrictional system of E. coli tF it has been comparatively studied with the already known modificational-and-restrictional systems isolated from various Escherichia coli strains. Results have shown that no identity exists between the tested systems and the one in E. coli tF. It is stated that the new modificational-and-restrictional system of E. coli tF belongs to none of the three known types of restrictional endonucleases.