Attenuation of Restriction

Streptomyces tendae ATCC 31160 produces nikkomycin, a fungicide and insecticide that inhibits chitin synthases. Exposure of S. tendae protoplasts to 50°C for 30 min is required for transformation (102 thiostrepton-resistant transformants ,ug of DNA-') with plasmid pU702 or pU680 from Streptomyces lividans. pU702 and pU680 DNA isolated from the S. tendae transformants is efficient (106 to 107 transformants ,ug of DNA-') in subsequent transformations of S. tendae protoplasts generated at 30°C. PstI fails to cut the single PstI site in pU702 and cuts only one of the two PstI sites in pU680 DNA isolated from S. tendae transformants. Digests of plasmid DNA mixtures showed that plasmid DNA from S. tendae does not inhibit PstI activity. pU702 and pIJ680 DNA from S. tendae transformants was used to transform S. lividans to show that plasmid DNA remains unchanged, except for modification at some PstI sites in S. tendae, as a consequence of passage through S. tendae. The DNA modification is lost when S. lividans is transformed with plasmid DNA from S. tendae transformants. Since S. tendae modifies only some PstI sites, it appears the modification (presumably restriction activity also) activity in S. tendae recognizes a sequence that includes or overlaps the PstI hexanucleotide recognition sequence.