Molecular Studies of R Factor Compatibility Groups

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Abstract
Molecular studies of R factors of six groups, FII, I1, I2, N, B, and H, defined on the basis of compatibility, support the conclusions drawn from genetic studies. In general, R factors of a given compatibility group are similar in size. Deoxyribonucleic acid (DNA) reassociation occurs freely between members of the same group but is minimal between heterologous groups. An exception to this was found in group H, of which one factor showed minimal homology with the remaining plasmids of the group. A further exception was found with groups I1 and B, which, although genetically distinct, show between 18 and 28% of DNA homology. Groups I1 and I2 are molecularly distinct, despite the fact that they both stimulate the synthesis of I-fimbriae.