(A) Primer extension assay, analyzed by denaturing acrylamide gel electrophoresis and [α-32P]dATP phosphorimaging. The wild-type polymerase domain of yeast Pol α was incubated at 37°C with poly(dT) 70mer template, dATP and either an oligo(A) or oligo(dA) 15mer primer (see ‘Materials and methods' for details). The reaction products were analyzed at the indicated time points. (B) Quantitative product size-distribution analysis of the primer extension assay in panel A. For each time point, the intensities of the RNA and DNA primer extension products were measured and normalized relative to the measured intensity of the 12mer product in the RNA primer lane. The normalized values of the RNA and DNA-primer extension products are plotted against the size of the extension product, as number of bases, in the top and bottom panels, respectively. The normalized values are the average of three independent measurements. (C) Primer extension assay. The catalytic domain of yeast Pol α and a recombinant version of the yeast Pol α/primase complex were incubated at 37°C and for 60 s with a poly(dT) 70mer template, dATP and either an oligo(A) or oligo(dA) of different length, as indicated in the panel. (D) Primer extension assay. The catalytic domain of yeast Pol α was incubated at 37°C and for 60 s with dATP and one of the following 5′-to-3′ primer/template pairs: A12, A12/(dT)50; dA12, (dA)12/(dT)50; 2 G, A5GGA5/T43CCT5; 4 G, AGGA2GGA5/T43CCT2CCT ; 6 G, AGGA2GGAGGA2/T40CCTCCT2CCT; 7 G, AGGAGGGAGGA2/T40CCTCCCTCCT.