The effectiveness of restriction endonucleases in cell killing and mutation.

The use of restriction endonucleases (RE) to study the importance of DNA break end structures in differential cellular response has proved controversial. The number of DNA cut sites and the accessibility of RE are recognized examples of confounding factors. We have eliminated these factors by comparing the effectiveness of isoschizomers. Additionally, we considered for the first time the tolerance of the enzymes to cellular conditions. Cell killing and mutation were compared to the overall cutting ability of the enzymes in an "intracellular" buffer. We found that the activity of each RE combined with its lifetime, under simulated cellular conditions, were the overriding factors in determining effectiveness.