Figure 2.

Coordination between the 3′–5′ exonuclease and polymerization activities of Nf and GA-1 DNA polymerases. The assay was carried out as described in Materials and Methods, using 0.18 ng of the 5′-³²P-labelled hybrid molecule sp1/sp1c+6 as primer/template DNA, 25 ng of DNA polymerase, and the indicated concentration of the four dNTPs. After incubation for 5 min at 30°C, samples were analysed by 8 M urea–20% PAGE and autoradiography. The 15mer position (non-elongated primer) and 21mer position (elongated primer) are indicated. Polymerization or 3′–5′ exonuclease activities are detected as an increase and decrease, respectively, in the size of the labelled sp1 primer.