SINGLE AMINO-ACID SUBSTITUTIONS UNCOUPLE THE DNA-BINDING AND STRAND SCISSION ACTIVITIES OF FOK-I ENDONUCLEASE

Single alanine substitution mutations at Asp-450 or Asp-467 of the typ e IIS restriction enzyme Fok I have no effect on the ability of the en zyme to bind strongly and selectively to its recognition site but comp letely eliminate its ability to cleave either strand of substrate DNA. Since wild-type Fok I shows no kinetic preference or required order o f strand cleavage, these results indicate that Fok I, which evidently functions as a monomer, uses a single catalytic center to cleave both strands of DNA. In this respect, Fok I may resemble other monomeric en zymes that cleave double-stranded DNA.