Structure and function of plasmid ColE1 and related plasmids

Analysis of plasmid ColE1, its naturally occurring relatives ColK and CloDF13, and a wide range of ColE1 derivatives containing either insertions or deletions of genetic material has allowed localization on the ColE1 genome of DNA sequences responsible for colicin E1 synthesis, immunity to colicin killing, conjugal mobility and incompatibility. We have examined incompatibility between pairs of ColE1 derivatives ranging in size from 2.6 to 13.8 Md. Though all the plasmids tested exerted ColE1 incompatibility, a definite pattern was observed regarding the dominant plasmid in any pair tested (i.e. the plasmid that displaces the other from a heterozygote). Usually the larger plasmid is displaced. We conclude that loci for incompatibility reside within 0.7 kb of the ColE1 replication region. A model is presented to explain both the incompatibility data and the observation that the fraction of total DNA occurring as ColE1-like plasmid in a cell is approximately constant. Transposons Tn1 and Tn3 (3.2 Md; Apr and approximately 85% homologous), Tn501 (5.5 Md; Hgr), and Tn7 (9.3 Md; Tpr Smr) can all be transposed into ColE1. Though all have closely related. Tn501 and Tn7 do not complement transposition of Tn3 transposition defective deletions. A Tn3-specified 19,000 dalton protein is absent in one particular class of transposition-defective deletion.