Single-strand regions of poly(G) act as templates for oligo(C) synthesis.

Oligonucleotide primers consisting of a sequence of four or more deoxycytidylate residues terminated by a single ribocytidylate residue are extended by reaction with cytidine 5'-phosphoro(2-methyl)imidazolide using polyguanylic acid as a template. The efficiency of the reaction decreases as the length of the primer increases. The reaction does not seem to depend on the dissociation of poly(G) tetrahelices but uses as templates single-stranded segments that are already present in enzymatically synthesized polyguanylic acid.