Bis-peptide nucleic acid (bis-PNA) binding results in D-loop formation by strand displacement at complementary homopurine stretches in DNA duplexes. Transcription and replication in intact cells is mediated by multienzymatic complexes involving several proteins other than polymerases. The behaviour of the highly stable clamp structure formed by bis-PNAs has thus far been studied with respect to their capacity to arrest RNA polymerases. Little attention has been given to their recognition and processing by DNA helicases. In this report we have investigated the inhibitory effect of a bis-PNA on the DNA-helicase activity of the well characterized herpes simplex type I UL9 protein. Unwinding by UL9 of a synthetic substrate is significantly inhibited by a bis-PNA and the addition of the ICP8 protein, which increases UL9 processivity, does not relieve this inhibition.
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