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Model DNA polymers containing heteroduplex regions of defined sequence and size were synthesized using polynucleotide phosphorylase and calf thymus terminal transferase. Heteroduplexes were of the form (dG)n-d(C12AmC-x), where m - 1-6, and (dG)n-d(C10GmC-x), where m = 1 and 3-5. Thermal melting studies of the model DNAs indicated that the heteroduplex regions did not disrupt the cooperative interaction between the flanking regions of dG-dC base pairs. thus, it is possible that the heteroduplex nucleotides are accommodated in a stacked helical structure.
Dodgson et al. (Tue,) studied this question.