We have studied the template-directed oligomerization on polycytidylic acid of the 5'-phosphoro(2-methyl)imidazolides of a number of analogues of guanosine. None of the analogues reacted as efficiently as the original guanosine compound, and only the 7-deazaguanosine analogue gives a detectable yield of oligomers. Similar results are described for a reaction involving the intramolecular template-directed elongation of a short oligocytidylate primer.Oligocytidylates containing five or more cytidylate residues are extended on the single-stranded regions of poly(G). In the present study we show that these oligo~ cytidylates are extended efficiently by reaction with cytidine-5'-phosphoro(2-methyl)imidazolide on a poly(7-deazaguanylic acid) template. The products are considerably longer than those obtained using a polyguanylic acid template. We believe that the formation of a tetrahelix inhibits the latter reaction, while poly(7-deazaguanylate) does not aggregate and, therefore, acts as a more efficient template. This work identifies for the first time a pair of homopolymers each of which facilitates the template-directed elongation of the other.
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.
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