[BsiI--a new unusual restriction endonuclease].

The restriction endonuclease BsiI from Bacillus sphaericus was isolated. The recognition sequence and cleavage point of enzyme BsiI have been determined as (sequence: see text). This restriction endonuclease is not an isoschizomer of any known restriction endonucleases and differs from other enzymes: it hydrolyses DNA into unsymmetrical recognition sequence.