Eukaryotic DNA Polymerases

Some significant differences between the processes of bacterial and eukaryotic replication are in the number and functions of DNA polymerases. Eukaryotic cells contain a number of different DNA polymerases that function in replication, recombination, and DNA repair.

Three DNA polymerases carry out most of nuclear DNA synthesis during replication: DNA polymerase α, DNA polymerase δ, and DNA polymerase ε (Table 9.4). DNA polymerase α has primase activity and initiates nuclear DNA synthesis by synthesizing an RNA primer, followed by a short string of DNA nucleotides. After DNA polymerase α has laid down from 30 to 40 nucleotides, DNA polymerase δ completes replication on the lagging strand. Similar in structure and function to DNA polymerase δ, DNA polymerase ε replicates the leading strand. DNA polymerase γ replicates mitochondrial DNA; a γ-like polymerase also replicates chloroplast DNA. Other specialized DNA polymerases, called translesion polymerases, are able to bypass bulky distortions in DNA structures that block the usual replicating polymerases. Still other DNA polymerases play a role in DNA repair and recombination (see Table 9.4).

TABLE 9.4 DNA polymerases in eukaryotic cells
DNA polymerase 5′→3′ polymerase activity 3′→5′ exonuclease activity Cellular function
α (alpha) Yes No Initiation of nuclear DNA synthesis and DNA repair; has primase activity
δ (delta) Yes Yes Lagging-strand synthesis of nuclear DNA, DNA repair, and translesion DNA synthesis
ε (epsilon) Yes Yes Leading-strand synthesis
γ (gamma) Yes Yes Replication and repair of mitochondrial DNA
ζ (zeta) Yes No Translesion DNA synthesis
η(eta) Yes No Translesion DNA synthesis
θ (theta) Yes No DNA repair
ι(iota) Yes No Translesion DNA synthesis
κ (kappa) Yes No Translesion DNA synthesis
λ (lambda) Yes No DNA repair
μ (mu) Yes No DNA repair
σ (sigma) Yes No Nuclear DNA replication (possibly), DNA repair, and sister-chromatid cohesion
Φ (phi) Yes No Translesion DNA synthesis
Rev1 Yes No DNA repair

Note: The polymerases listed at the top of the table are those that carry out DNA replication.

CONCEPTS

There are a large number of different DNA polymerases in eukaryotic cells. DNA polymerases α, δ, and ε carry out replication on the leading and lagging strands. Other DNA polymerases replicate organelle DNA, carry out DNA repair, and help bring about recombination.