Transformation andPhysical Properties of R-Factor RP4Transferred fromEscherichia coli toRhizobium trifoii

mul-tiple drugresistance aftertheacquisition oftheR-factor. Transformation of R-factors has onlybeen reported on one previous occasion whenCohen et al. (3) transformed E. coli usingpurified R-factor DNA isolated from E. colistrains carryingI-like andF-like R-factors. Themaximalfrequencyoftransformationwasfound