Figure 6.

Schematic representation of the extension of a p(dG)₃G primer by reaction with l-2-MeImpG (G*). (a) On a d(C₈) template. Pyrophosphate formation is the main reaction, presumably because the primer and the l-2-MeImpG residue can be accommodated on a continuous sequence of d-residues of the template. (b) On d-l mixed oligo(dC) templates that have sequences d(C₄XC₄), where X is a sequence beginning with l-dC; once the primer occupies its most stable position on the template, there is no place to accommodate an additional l-2-MeImpG residue at the 3′ terminus of the template.