7 Fidelity of DNA Replication

Abstract

The six billion nucleotides of the diploid human genome are replicated in only a few hours while generating so few errors that the spontaneous mutation rate may be less than 1 mutation per genome per cell division (Loeb 1991). This incredible accuracy results from three major error-avoidance processes: the high selectivity of DNA polymerases, exo-nucleolytic proofreading, and postreplication mismatch repair. In this chapter, we review our current understanding of the first two of these processes. Readers interested in eukaryotic mismatch repair are referred to a recent review (Modrich 1994).

We begin by describing the steps in the polymerization reaction cycle that discriminate against base substitution errors, then review studies of the substitution fidelity of the five classes of eukaryotic DNA polymerases. We then consider several ways to make errors by template-primer slippage and review what is known about eukaryotic DNA polymerase frameshift error rates. Finally, we present information on the fidelity with which the multiprotein replication machinery replicates undamaged DNA and DNA containing adducts of known carcinogens.

BASE SUBSTITUTION FIDELITY
Discrimination Steps in a Polymerization Cycle
The error discrimination steps that operate during incorporation of a single nucleotide have been worked out primarily with prokaryotic and viral DNA polymerases. The steps (Fig. 1) include binding of the polymerase to the DNA, formation of a ternary complex with the incoming deoxyribonucleoside triphosphate (dNTP), a conformational change in this complex to position the substrates for phosphodiester bond formation, the chemical reaction step to form the bond, a second conformational change following the...