A Nucleic Acid Triple Helix Formed by a Peptide Nucleic Acid-DNA Complex

Science  15 Dec 1995:
Vol. 270, Issue 5243, pp. 1838-1841
DOI: 10.1126/science.270.5243.1838


The crystal structure of a nucleic acid triplex reveals a helix, designated P-form, that differs from previously reported nucleic acid structures. The triplex consists of one polypurine DNA strand complexed to a polypyrimidine hairpin peptide nucleic acid (PNA) and was successfully designed to promote Watson-Crick and Hoogsteen base pairing. The P-form helix is underwound, with a base tilt similar to B-form DNA. The bases are displaced from the helix axis even more than in A-form DNA. Hydrogen bonds between the DNA backbone and the Hoogsteen PNA backbone explain the observation that polypyrimidine PNA sequences form highly stable 21 PNA-DNA complexes. This structure expands the number of known stable helical forms that nucleic acids can adopt.

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