Abstract
Plasmid pSG1 is maintained in some derivatives of Streptomyces griseus NRRL3851 mainly in the chromosomally integrated form (pSG1 int ). In others, the integrated plasmid is co-maintained with free pSG1 [Cohen et al., Plasmid 13 (1985) 41–50]. The pSG1 plasmid integration site ( attP) and the pSG1 int -chromosome boundaries ( attL and attR) were cloned and sequenced. The results indicate that pSG1 int is flanked at attL by a functional tRNA ser gene and at attR by a 60-nt sequence of the 3' end of the same tRNA ser gene. A single mismatch distinguishes the 60-nt sequence at attR from its direct repeat at attL. The attP site contains a single copy of the 60-nt repeat, identical to the one at attL. This observation indicates that pSGl, like integrating plasmids of other Actinomycetes, is integrated in a tRNA gene and suggests that the exact excision of pSG1 int occurs by a recombinational crossing-over event at the first 43 nt of the 60-nt repeat.
Published Version
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