Figure 6: The effect of 3-deazaadenine (c3A) and 3-methyl-3-deazaadenine (3-m-c3A) lesions on (a) T7 Sequenase and (b) Klenow fragment polymerization. The template strand with an A, c3A or 3-m-c3A at position-27 (X) was incubated for 2.5, 5, 10 or 20 minutes with polymerase at 37°C using DNA to enzyme ratios of 200:1 or 20:1 for T7 Sequenase, and 50 : 1 or 5 : 1 for Klenow fragment (exo), respectively. Lanes with primer-20 + polymerase + template, and primers-20 and -25 (no polymerase or template) are included as markers. There is evidence for bands indicating stalling of polymerization with the c3A and a quantitative block with 3-m-c3A, which is also reflected in the extended product.