FIG. 3.

Deletion frequency in H. pylori wild-type and mutant strains. The chloramphenicol/kanamycin resistance cassette flanked by identical repeats (IDS) of 0, 50, or 100 bp was inserted into vacA (control) or mutS2, insertion was confirmed, and deletion frequencies were calculated, as described previously (8). Asterisks indicate that no deletions were detected (frequency < 10⁻⁸). As expected (8), H. pylori strains with the cassette in vacA or mutS2 showed progressively higher deletion frequencies with increasing size of the IDS. Strains with the deletion cassette in mutS2 do not show any significant difference in deletion frequency between flanking DNA repeats of 50 and 100 bp compared to control (vacA) mutants with comparable cassettes. Bars represent means ± standard deviations for four to six replicate experiments.