Gross chromosomal rearrangements in spontaneous bald mutants from S. avermitilis wild-type (WT) strain ATCC31267. (A) Ase I restriction map of wild-type chromosome. (B and C) Ase I restriction patterns of genomic DNA of bald mutants (SA). (D) Similar Ase I profiles of 76-9 and SA1-8. PFGE conditions for separating large fragments were: (B and D) 1.2% agarose, 4.5 V/cm, 20-130 s pulses, 36 h; 4.5 V/cm, 60-90 s pulses, 2 h; 4.5 V/cm, 5-10 s pulses, 8 h; conditions for separating small fragments were: (C) 1.5% agarose, 6 V/cm, 5-10 s pulses, 24 h. Fragments D and E overlapped because of their extremely similar migration; overlap was also found for fragments G1/G2, O/P/N, and S/T. SAP1: 94.3-kb linear plasmid. Solid arrows: missing fragments; Open arrows: potential missing fragments; Triangles: new bands.