CHARACTERIZATION OF A XHOI ISOSCHIZOMER IN STREPTOMYCES-AUREOFACIENS AFTER ACTINOPHAGE INFECTION

After infection of tetracycline producing strains of S. nui-eoSnciens with actinophages mu l/6 and Bl some phage resistant colonies were obt ained in each experiment. These colonies expressed a new restriction-m odification (RM) system of type II, which was different from the commo n RIM 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. aure ofaciens B96, using two step column chromatography to the grade withou t non-specific nucleolytic activity. SauLPII endonuclease recognized a nd cleaved the palindromic hexanucleotide sequence 5'-C/TCGAG-3', thus it was a true isoschizomer of XhoI.