Isolation and characterization of a type II restriction endonuclease from Streptococcus thermophilus

A type II restriction endonuclease Sth134I was isolated from Streptococcus thermophilus strain 134. The enzyme is an isoschizomer of HpaII. The restriction endonuclease is most active at Mg(II) greater than or equal to 5 mM; in the pH range of 7.5-8; temperature of 50 degrees-55 degrees C; and (KCl) or (NaCl) below 100 mM. Double digestion and ligation experiments showed that Sth134I apparently recognized and cleaves DNA at the sequence C1CGG to produce two-base, 5'-protruding ends.