Axis of Symmetry in DNA Sequences Most restriction enzymes bind to specific sequences in DNA (restriction sites) that are symmetrical about their mid points. The figure shows the restriction site for the enzyme EcoRI on DNA. The axis of symmetry does not imply that the enzyme cuts along that axis, as we will now see.

Restriction Cutting Sites Depending on the enzyme, the cut can occur in one of three ways, as illustrated in thefigures below. Animate each of these cleavage sites by clicking on the illustration. EcoRI PstI SmaI

These overhangs are very useful in linking two pieces of DNA together, as shown on the right. In fact this is the basis for recombinant DNA technology.

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