Streptomyces chusanensis ZS-2, isolated from a soil sample in Chusan of Taiwan, was found to produce a new Type II restriction endonuclease. This restriction enzyme was designated as SchI. The purified enzyme was characterized to be a homodimer with a subunit molecular weight of 28 kDa. It was apparently free from exonuclease activities. It cleaves the phosphodiester bond between the 4th "C" and the 5th "G" on the 5'- CCGCGG-3' sequence of DNAs leaving a 2-nucleotide protruding end at its 3' site. This data suggests that SchI is an isoschizomer of SacII. In addition, based on the comparison between SchI and SacII regarding of reaction parameters, it seems that SchI is a better choice of restriction enzyme for genetic analysis and mapping.
