Bacterial   restriction  enzymes  cut  DNA  at  recognition  sequence,
   producing complementary sticky ends.
   Enzymes  with  a four-base recognition sequence such as TaqI will cut,
   on average, every 256 (4^4) base pairs.
   EcoRI  has  a  six-base  recognition  sequence,,  and  produce average
   fragments of 4096 (4^6) base pairs.