Restriction endonucleases: general survey procedure and survey of gliding bacteria

Among 120 strains of gliding bacteria which were screened for restriction endonucleases, 27 were found positive. Additionally, three strains carried enzymes able to release the supercoiled state of closed circular DNA. By using a new rapid method, restriction endonuclease activity was released by stirring about 0.5 g of cells (fresh weight) in a motor-driven glass homogenizer in buffer containing Triton X-101, ethylenediaminetetraacetic acid, and mercaptoethanol. A yield from 60 to 80% of the total activity present in the cells was obtained with minimal destruction of the cells. The enzyme activity in the crude extract was measured semi-quantitatively by digestion of DNA and subsequent separation of the fragments on an agarose slab gel. The method appears to be generally applicable for the extraction of restriction endonucleases from gram-negative bacteria on an analytical scale and in a modified form for large-scale preparation of restriction enzymes.