Isolation and identification of the restriction endonuclease PtaI from Phormidium tadzschicicum, an isoschizomer of BspMII.

Ptal is a type II restriction endonuclease from the Cyanobacterial strain Phormidium tadzschicicum. This strain was obtained from the Collection of Algal Cultures of Leningrad University. Ptal recognizes the sequence 5'-TCCGGA-3' and cleaves between T and C. The enzyme was purified using the following chromatographic steps: 1) Phosphocelulose, 2) DEAESephadex. The enzyme was free of contaminating nucleases. Optimal conditions for Ptal digestion are 20 mM Tris (pH 7.9), 10 mM MgCl2, 50 mM KC1, 100 /jg/ml BSA, 1 mM DTT and incubation at 37 °C. Ptal cleaves lambda DNA giving the same digestion pattern as BspMII. DNA sequencing (Figure 2) confirmed that Ptal is an isoschizomer of BspMII. ACKNOWLEDGMENTS