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λ Bacteriophages produced inEscherichia coli C (designated as λ · C) are restricted in their ability to grow inE. coli K-12. The rare successful infections that arise in the K-12 population occur in “special” cells which have lost their capacity to restrict λ · C. These infections yield modified progeny phage (designated as λ · K) which, unlike λ · C, plate equally well onE. coli C andE. coli K-12. When methionine, but no other amino acid, was removed from the growth medium of a mutant strain ofE. coli K-12, the number of special cells rapidly increased 500- to 3,000-fold. These new special cells retain their capacity to produce modified λ · K progeny. This conversion of restricting cells into special cells does not require the synthesis of new protein. The special cells formed when methionine was removed from the culture did not revert into restricting cells when methionine was restored. Such cells have also lost the ability to divide for at least 4 hr after methionine supplementation. When methionine was restored, the remaining restricting cells, but not the special cells, immediately resumed growth. Removing methionine from cultures ofE. coli B caused a similar increase in the number of special cells able to support the growth of λ · C and λ · K. However, whenE. coli K-12 (P1) cultures were deprived of methionine, the number of special cells increased for λ · C but not for λ · K. Thus, retention of the P1-restriction system, unlike the B- and the K-12-systems, does not require the presence of methionine.

Loss of Host-controlled Restriction of λ Bacteriophage in Escherichia coli Following Methionine Deprivation