A comparison of DNA cleavage by the restriction enzymes SalPI and PstI

Methods for obtaining highly active, exonuclease-free, stable preparations of the Streptomyces albus P restriction enzyme SalPI are described. SalPI and its isoschizomer PstI (from the taxonomically distant Providencia stuartii 164) both cleave their recognition sequence (5'-CTGCAG-3') to generate fragments terminating in tetranucleotide 3' extensions whose sequence is 5'-TGCA-3'. Bacteriophage R4G2 DNA, protected against SalPI cleavage by pregrowth on S. albus P, is also protected against PstI cleavage; and total DNA of both S. albus P and P. stuartii 164 is resistant to cleavage by both enzymes.