Colicin factors and Episomes

Abstract

Frequency of transfer of colicinogeny for El (colEl+) to W677 non colicinogenic recipient cells from (colEl+) Hfr cells of types Hayes, Cavalli, Reeves 1, AB313, P4X and P10 was unrelated to origine and direction of Hfr transfer, and time of entry was 7-12 mins in all crosses. Lethal zygosis was found in similar crosses of same Hfr strains when neither parent was colicinogenic, provided a high HfrF[image] ratio was used. Less than 1% of the recipient cells survived after mating at 20:1 Hfr:F~ ratio using Hfr Hayes and Cavalli, but there was no killing at any ratio using Hfr P10. This lethal zygosis is concluded to be unrelated to colEl transfer, which is assumed to take place cytoplasmically and not chromosomally. ColEl and other colicin factors are concluded to be plasmids rather than episomes.