THE ARD GENE ENCODING THE TYPE-I RESTRICT ION INHIBITOR IS PRESENT INCONJUGATIVE PLASMIDS OF FII, B O, AND K-GROUPS OF INCOMPATIBILITY/

The effect of conjugative plasmids of various incompatibility groups o f the enterobacteria family on the activity of the cell restriction-mo dification system of type I (EcoK) was studied. Twenty-two conjugative plasmids of 15 incompatibility groups were tested. In addition to pla smids of the incI1 and incN groups studied earlier, conjugative plasmi ds of the incFII, incB/O, and incK groups were also shown to be able t o weaken the action of type I restriction enzymes upon nonmodified DNA (Ard phenotype). A hybridization analysis of all the plasmid DNAs stu died, using ard gene DNA sequences from the ColIb-P9 (incI1) plasmid a s a probe, was performed. The ard locus of the R100 (incFII) plasmid w as cloned in the pBR322 and pACYC184 vectors. The ard gene was located 2.5 kb from the oriT site in the leading region on the R100 conjugati ve plasmid.