FIG. 1.

(A) Plasmid preparation by the alkali lysis method from strains 537, which carries pJS-B (lane 1, native plasmid; lane 3, plasmid cleaved with ClaI), and strain 2375, which is lacking the plasmid (lane 2). (B) Southern blot demonstrating plasmid pJS-B in its chromosomal and its plasmid forms in strains 537 and 2375. Chromosomal DNA was digested with ClaI-BamHI (lanes 1) or with ClaI-EcoRV (lanes 2). (C) Probe 48/49 covered positions 1400 through 2382 of the plasmid, and probe 43/50 covered positions 5252 through 558. Thus, only probe 43/50 contained the ClaI recognition site of the plasmid (position 6811). The hybridization patterns obtained with the two strains were identical, except for the linearized plasmid band, which appeared only in strain 537 (arrow). The remaining bands were due to hybridization of the probes to the chromosomal copy of pJS-B present in both strains. The position of the inverted repeat region IR1/IR2 of the plasmid is indicated.