NUCLEOTIDE-SEQUENCE OF A NICKING SITE OF THE STREPTOMYCES PLASMID PSN22 REPLICATING BY THE ROLLING CIRCLE MECHANISM

A putative nicking site in the double strand origin (DSO) of the Strep tomyces plasmid pSN22 was identified by comparing the nucleotide seque nce of the DSO region with those of two other Streptomyces plasmids, p IJ101 and pJV1. A 7-bp sequence of this putative nicking site, 5'-CTTG GGA-3', was similar to the consensus sequence of the nicking site of t he pC194 group of plasmids. When several point mutations were introduc ed into this 7-bp sequence, the transformation abilities of the mutant plasmid molecules for Streptomyces lividans were either reduced or lo st. Southern hybridization analysis indicated that these mutant plasmi ds could not replicate in S. lividans, but were integrated into the ch romosomal DNA.