Nucleic Acids Research, 2002, Vol. 30, No. 4 950-957
© 2002 Oxford University Press
Non-WatsonCrick interactions between PNA and DNA inhibit the ATPase activity of bacteriophage T4 Dda helicase
Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, 4301 West Markham Street, Little Rock, AR 72205, USA and 1Department of Pharmacology and Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX 75390-9041, USA
Peptide nucleic acid (PNA) is a DNA mimic in which the nucleobases are linked by an N-(2-aminoethyl) glycine backbone. Here we report that PNA can interact with single-stranded DNA (ssDNA) in a non-sequence-specific fashion. We observed that a 15mer PNA inhibited the ssDNA-stimulated ATPase activity of a bacteriophage T4 helicase, Dda. Surprisingly, when a fluorescein-labeled 15mer PNA was used in binding studies no interaction was observed between PNA and Dda. However, fluorescence polarization did reveal non-sequence-specific interactions between PNA and ssDNA. Thus, the inhibition of ATPase activity of Dda appears to result from depletion of the available ssDNA due to non-WatsonCrick binding of PNA to ssDNA. Inhibition of the ssDNA-stimulated ATPase activity was observed for several PNAs of varying length and sequence. To study the basis for this phenomenon, we examined self-aggregation by PNAs. The 15mer PNA readily self-aggregates to the point of precipitation. Since PNAs are hydrophobic, they aggregate more than DNA or RNA, making the study of this phenomenon essential for understanding the properties of PNA. Non-sequence-specific interactions between PNA and ssDNA were observed at moderate concentrations of PNA, suggesting that such interactions should be considered for antisense and antigene applications.
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