When SXT excises form the chromosome, it doesn t leave a copy of the element behind. Therefore, recA must be required for transfer of the element to the recipient. A mutation in int resulted in no formation of the circular intermediate, and consequently no transfer of the SXT element. If int was supplied on a plasmid, transfer of SXT element was restored. Therefore, it was determined that int had function in the excision or circularization of the element as well as integration of SXT into the host chromosome.
Many conjugative transposons can mobilize plasmids from the host cell.
To test if the SXT element could also mobilize plasmids, Hochhut and Waldor monitored the frequency of transfer of a plasmid containing a KanR cassette. It was found that this plasmid was transferred, but the frequency of transfer was reduced approximately100 fold that of SXT transfer. In addition, transfer of Kan and SXT were independent of each other. Therefore, it was concluded that the transfer of SXT and the plasmid where independent functions. An int minus donor was found to transfer the plasmid at the same frequency.