Characterization of circular chromosome in SA1-6. (A) Schematic representation of the chromosomes of wild-type strain and mutant SA1-6, showing deletions at both ends. (B) Location of chromosomal deletion ends and fusion junction. Bg, Bgl II. (C) Southern analysis of fusion fragment with probe N4, which was prepared using primers 405 and 406. (D) Junction sequence, showing no obvious homology between the original sequences.