Connection between foreign DNA replication and induced expression of the restriction-modification system in Streptomyces aureofaciens.

Tetracycline-producing strains of Streptomyces aureofaciens expressed SauLPI restriction-modification (R-M) system, which recognized specific DNA sequence 5'-GCCGGC-3' (isoschizomer Nael). The activation of the second R-M system SauLPII (5'-GAGCTC-3', isoschizomer of XhoI), which was silent during the growth cycle, after a foreign DNA transfer into this strain was observed. This phenomenon was tentatively explained as a response of the cells against the exogenous DNA entering the cells. The involvement of a SOS-like response in induction of R-M system genes in S. aureofaciens strains has been considered.