MICROBIAN GENETICS: REVERSIBLE INTEGRATION OF THE F' SEX EPISOME IN ESCHERICHIA COLI K 12
ARMY BIOLOGICAL LABS FREDERICK MD
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Some clones, Hfr, were selected, either at high temperature or at low temperature in the presence of acridine on the basis of mutated bacteria whose F episome does not multiply at high temperature in the autonomous state. The integration mechanisms of the episome and of the chromosomal transfer by I strains may be deduced from the properties of these strains. The sex episome of Escherichia coli K 12, in the autonomous state, confers on the bacterium that carries it F the capability of being paired with a bacterium F- and of transferring episome F to it at high frequency. The integration of the episome and of the chromosome creates a new type of male bacterium Hfr, which transfers an oriented group of chromosomal genes at high frequency, but does not transfer the autonomous episome F. A third sexual type, intermediary type I, has also been observed recently. The I bacteria transfer the episome by crossing the autonomous state with the same efficacy as the F bacteria. Like the Hfr bacteria, on the other hand, but with a ten times lower frequency, they transfer a characteristic chromosomal sequence. All these characteristics are acquired simultaneously by the bacteria that receive the episome of an I bacteria modified episome F by conjugation.