PFGE analysis of the chromosomes of S. avermitilis strains. (A) PFGE of intact chromosome treated with Proteinase K (PK) and SDS. (B) PFGE analysis of Ase I digested chromosome with PK and SDS treatment, showing that fragment NA2 is a new end bound to terminal protein. PFGE conditions for (A) were: 1% agarose, 3 V/cm, 180 s pulses, 20 h. Conditions for SA1-8 and wild-type in (B) were the same as for Fig 1B and 1C, respectively. "+" represents DNA sample treated with PK; "-'' represents DNA sample treated with SDS.