Abstract
An important not yet fully understood event in DNA replication is the DNA polymerase (pol) switch from pol α to pol δ. Indirect evidence suggested that the clamp loader replication factor C (RF-C) plays an important role, since a replication competent protein complex containing pol α, pol δ and RF-C could perform pol switching in the presence of proliferating cell nuclear antigen (PCNA). By using purified pol α/primase, pol δ, RF-C, PCNA and RP-A we show that: (i) RF-C can inhibit pol α in the presence of ATP prior to PCNA loading, (ii) RF-C decreases the affinity of pol α for the 3′OH primer ends, (iii) the inhibition of pol α by RF-C is released upon PCNA loading, (iv) ATP hydrolysis is required for PCNA loading and subsequent release of inhibition of pol α, (v) under these conditions a switching from pol α/primase to pol δ is evident. Thus, RF-C appears to be critical for the pol α to pol δ switching. Based on these results, a model is proposed in which RF-C induces the pol switching by sequestering the 3′-OH end from pol α and subsequently recruiting PCNA to DNA.
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