3 SITE-SPECIFIC ENDONUCLEASES FROM THERMOPHILIC STRAIN BACILLUS SPECIES LA ARE ISOSCHIZOMERS OF HHAI, ASUII, AND HINDIII

Screening of thermophilic bacterial strains revealed a strain containi ng three site-specific endonucleases: BspLAI, BspLAII, and BspLAIII. T hese endonucleases were purified to functional purity by sequential ch romatography. Recognition sites, DNA cleavage sites, and some properti es of the endonucleases were determined. BspLAI recognizes the sequenc e 5'-GCG down arrow C-3' on the DNA molecule and is an isoschizomer of endonuclease HhaI. BspLAII recognizes the sequence 5'-TT down arrow C GAA-3' and is an isoschizomer of AsuII. BspLAIII recognizes site 5'-A down arrow AGCTT-3' and is an isoschizomer of endonuclease HindIII. Al l the three enzymes exhibit maximal activity at 55 degrees C. The opti mal buffer is MRB, pH 7.4. They retain activity on storage for 3 weeks at room temperature and thus are highly stable.