Isolation, mapping, and examination of effects of TnA insertions in ColE1 plasmids.

Twelve TnA insertions of ColE1 deoxyribonucleic acid have been isolated and mapped by electron microscopic studies of heteroduplex molecules. Insertions only blocking the production of active colicin clustered in one region of the map, whereas insertions only blocking the expression of deoxyribonucleic acid nicking activity associated with the plasmid "relaxation complex" clustered in another region of the map. The location of one insertion that blocks both the expression of colicin immunity and the production of active colicin suggests that the expression of both characteristics are coordinately controlled.