Unrelated conjugative plasmids have sequences which are homologous to the leading region of the F factor.

Conjugative plasmids from various incompatibility groups which carry DNA homologous to the ssb gene of the F factor were found to have additional homology with the F factor. This region homologous with F was located on both sides of the ssb gene and occupied a considerable part of the leading region, i.e., the 12.9-kilobase portion of F transferred first during conjugation. This region was the only region of the F factor which has a homologous counterpart on many plasmids.