FIG. 1.
Genes required for SXT integration. Integration of replication-deficient plasmids containing the SXT attP site was assessed by a conjugation assay. The inserts in these plasmids, all of which were derived from the mobilizable suicide vector pGP704, are indicated. In the diagrams of the inserts, open reading frames are indicated by arrows, the SXT attP site is indicated by a black box, the putative promoter region upstream of the int-containing operon is indicated by a gray box with an arrow, and the frameshift mutations are indicated by x's. The frequency of exconjugant formation was obtained by dividing the number of exconjugants (Tcr Apr CFU) by the number of recipients (Tcr CFU). In all the cases, the donor strain was E. coli SM10λpir and the recipient strains were E. coli CAG18439 derivatives. For the plasmids in panel A, the recipient cells harbored pSetCD33, which contained setCD under control of PBAD. For the plasmids in panel B, the recipient cells harbored pInt33, which contained int under control of PBAD. To induce expression of setCD or int, the conjugation assays were carried out by using media supplemented with 0.02% arabinose. The bars indicate the mean values obtained from two independent experiments. The asterisk and the circle in lines 3 and 4 indicate that the frequencies of exconjugant formation were less than 10−5 exconjugant/recipient; in line 3, the frequency was 9.7 × 10−6, and in line 4, the frequency was 7.0 × 10−6.