Three site-specific endonucleases from thermophilic strain Bacillus species LA are isoschizomers of HhaI, AsuII, and HindIII.

Screening of thermophilic bacterial strains revealed a strain containing three site-specific endonucleases: BspLAI, BspLAII, and BspLAIII. These endonucleases were purified to functional purity by sequential chromatography. Recognition sites, DNA cleavage sites, and some properties of the endonucleases were determined. BspLAI recognizes the sequence 5-GCG/C-3 on the DNA molecule and is an isoschizomer of endonuclease HhaI. BspLAII recognizes the sequence 5-TT/CGAA-3 and is an isoschizomer of AsuII. BspLAIII recognizes site 5-A/AGCTT-3 and is an isoschizomer of endonuclease HindIII. All the three enzymes exhibit maximal activity at 55 degrees C. The optimal buffer is MRB, pH 7.4. They retain activity on storage for 3 weeks at room temperature and thus are highly stable.