Abstract
DNA and RNA polymerases are enzymes that are primarily responsible for copying genetic material in all living systems. The four polymerases whose structures have been determined by X-ray crystallographic methods have significant similarities at the polymerase active site that are indicative of common requirements for polynucleotide synthesis. Structural studies of complexes of the Klenow fragment of
Escherichia coli DNA polymerase I, HIV type 1 reverse transcriptase, and rat DNA polymerase β with DNA are leading to generalized models for catalysis.