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SUMMARY When a strain of Escherichia coli lysogenic for h and deleted for the gal operon was infected with hdg two types of gal+ transductants arose, an expected class with enzyme levels similar to wild-type, and a exceptional class with elevated levels of enzyme and altered staining reactions on indicator plates. Transductants of the exceptional class appear to carry multiple copies of a homoimmune hdg prophage. When exceptional transductants were prepared carrying a ts kinase mutation in their hdg and then selected for ability to grow at high temperatures, two types of hdg could subsequently be isolated from the temperature-resistant revertants, one carrying a temperat ure-resistant and the other a temperature- sensitive kinase gene. It has been possible to infer the existence of polytransductants containing more than two transducing prophage by their segregation patterns. The rate at which such cells produce phage, after U.V. induction, in a medium with galactose as the sole carbon source, is accounted for by the polytransductant structure. Polytransductant cells arose following infection by hdg at very low multiplicities. Identification of prophage types after mixed infection with genetically marked hdg's showed that each polytransductant carried only one type of transducing phage. When the superinfecting transducing phage was unable to make active h repressor, as is the case for hpg,C,857 at high temperature, the frequency of polytransductant formation was enhanced. Inhibition of protein synthesis with chloramphenicol also enhanced polytransductant formation. These experiments suggest that, at least in the case of Ad,, limited phage replication does take place in immune hosts, and is followed by multiple integrations into the bacterial chromosome.

Polytransductant Formation in Escherichia coli Lysogens