Characterization of a XhoI isoschizomer in Streptomyces aureofaciens after actinophage infection.

After infection of tetracycline producing strains of S. aureofaciens with actinophages mu 1/6 and B1 some phage resistant colonies were obtained in each experiment. These colonies expressed a new restriction-modification (RM) system of type II, which was different from the common RM system (SauLPI) of these strains recognizing the sequence GCCGGC. This new RM system was not detected before in parental strains. The new endonuclease was purified from a phage resistant strain of S. aureofaciens B96, using two step column chromatography to the grade without non-specific nucleolytic activity. SauLPII endonuclease recognized and cleaved the palindromic hexanucleotide sequence 5'-C/TCGAG-3', thus it was a true isoschizomer of XhoI.