The F plasmid carries an IS3 insertion within finO.

DNA-DNA hybridization studies support the conclusion that coding sequences of the fertility inhibition gene, finO, are present on the F plasmid and map downstream of the transfer region, entirely within 99.19-2.0 F. In addition, the results indicate that the IS3a element at 100/0-1.26 F is inserted within the F finO coding region. This insertion may have inactivated the finO gene on the F plasmid.