DNA unzipped under a constant force exhibits multiple metastable intermediates

TL;DR

This study investigates how double-stranded DNA unzips under constant force, revealing multiple metastable intermediates and sequence-dependent pauses, with implications for understanding DNA replication dynamics.

Contribution

It provides experimental evidence of sequence-dependent metastable intermediates during DNA unzipping under constant force, a phenomenon previously uncharacterized.

Findings

Reproducible pause positions across multiple molecules indicate sequence dependence.

Unzipping times vary with applied force, from hours to less than 30 minutes.

DNA exhibits metastable intermediates during unzipping under constant force.

Abstract

Single molecule studies, at constant force, of the separation of double-stranded DNA into two separated single strands may provide information relevant to the dynamics of DNA replication. At constant applied force, theory predicts that the unzipped length as a function of time is characterized by jumps during which the strands separate rapidly, followed by long pauses where the number of separated base pairs remains constant. Here, we report previously uncharacterized observations of this striking behavior carried out on a number of identical single molecules simultaneously. When several single lphage molecules are subject to the same applied force, the pause positions are reproducible in each. This reproducibility shows that the positions and durations of the pauses in unzipping provide a sequence-dependent molecular fingerprint. For small forces, the DNA remains in a partially unzipped state for at least several hours. For larger forces, the separation is still characterized by jumps and pauses, but the double-stranded DNA will completely unzip in less than 30 min.