Three overstretched DNA structures confirmed

A team of researchers led by Associate Professor Yan Jie from the Department of Physics at the National University of Singapore (NUS) Faculty of Science has identified three new distinct overstretched deoxyribonucleic acid (DNA) structures caused by mechanical stretching. This discovery provides a clear answer to a long-running debate among scientists over the nature of DNA overstretching.

Debate on Possible DNA Structural Transitions

Recent single-molecule studies revealed that mechanical stretching could induce transitions to elongated DNA structures. Three possible elongated DNA structures have been proposed, namely: a single-stranded DNA under tension, DNA bubbles consisting two parallel, separated single-stranded DNA under tension, and a new form of base-paired double-stranded DNA. The existence of the three transitions has been heavily discussed among scientists for some 17 years.

To fully understand the nature of DNA overstretching, the team led by Assoc Prof Yan, which comprises members from NUS, the University of Minnesota and the Massachusetts Institute of Technology, explored the possible structural transitions.

Three Distinct Transitions Revealed

In their recent study, the researchers systematically investigated the three possible transitions induced by mechanical stretching, with methods to control DNA construct, temperature, force and salt concentration. Their data successfully identified all the three proposed structures and fully characterised their respective thermo-mechanical properties. These findings were first published on the online version of the Proceedings of the National Academy of Sciences on 19 February 2013. These findings complete the picture about the structures of DNA under tension, providing a conclusion to the 17-year-old debate.

Biological Implications and Potential Applications

As forces over a wide range are present in the DNA of cells, the researchers' findings provide new perspectives of possible force-dependent regulations of critical biological processes, such as DNA damage repair and gene transcriptions.

In addition, as many recently developed DNA devices are based on thermo-mechanical properties of various DNA structural motifs, these findings may also have potential applications in designing new DNA devices for the future.

The Next Step

To further their research, Assoc Prof Yan and his team will study the physiological functions of the three overstretched DNA structures, and investigate the presence of any new DNA structures under other mechanical constraints.