SUMMARY: A fertile mutant isolated from LT-7 with a mutator gene was found to have a high recipient ability when used as a recipient of the chromosome and F’ and R factors, whereas LT-7 and LT-2 , both of which lack the gene, were poor recipients of these foreign deoxyribonucleic acids, LT-7 exhibited an intermediate recipient ability. These episomal elements, however, were transferred from LT-7 and LT-7 to the , and substrains at frequencies comparable to an recipient. In contrast, the frequencies of transfer of these episomes from LT-7 to the other substrains of were considerably lower than those to LT-7. The efficiencies of plating of phage P-22 grown on LT-7 were likewise lower on LT-7, LT-7 and LT-2 than on LT-7. The of phage P-22 on LT-7, LT-7 and LT-7 were increased to the value on LT-7 by its growth on LT-7 or LT-2 . The frequencies of transduction of an R factor to these substrains of with phage P-22 grown on various substrains were parallel with the of this phage on these strains. It was further shown that the deoxyribonucleic acid of phage P-22, which had previously been propagated on LT-7, injected into LT-7 and LT-2 is rapidly degraded, whereas appreciable breakdown did not occur in LT-7. These results with P-22 indicate that LT-7 is a mutant which is impaired in its capacity of restriction and modification of this phage. The growth of P-22 on LT-7 resulted in partial increase of its on LT-7 and LT-2 , indicating that the restriction and modification capacities of LT-7 are partially affected. The above results, that LT-7 acts as a good recipient in the conjugal transfer of chromosome and non-viral episomes and that the frequencies of transfer of the non-viral episomes among the substrains of are comparable to those to LT-7 and are interpreted as due to the restriction- and modification-less nature of LT-7.


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