Restriction of a bacteriophage of Streptomyces albus G involving endonuclease SalI

Abstract

The bacteriophage Pal6, isolated from soil on S. albus G, was restricted when transferred from an alternative host back to S. albus G. Extracted unmodified Pal6 DNA was cleaved at a single site by a cell-free extract of S. albus G. Fractions cleaving Pal6 DNA contained the endonuclease SalI first described by J. Arrand, P. Myers and R. J. Roberts (unpublished data). A mutant of S. albus G was isolated which was defective in both restriction and modification of Pal6. This mutant lacked SalI activity. SalI is apparently the agent of restriction of Pal6 by S. albus G.