Directing Uphill Strand Displacement with an Engineered Superhelicase

The ability to finely tune reaction rates and binding energies between components has made DNA strand displacement circuits promising candidates to replicate the complex regulatory functions of biological reaction networks. However, these circuits often lack crucial properties, such as signal turnover and the ability to transiently respond to successive input signals that require the continuous input of chemical energy. Here, we introduce a method for providing such energy to strand displacement networks in a controlled fashion: an engineered DNA helicase, Rep-X, that transiently dehybridizes specific DNA complexes, enabling the strands in the complex to participate in downstream hybridization or strand displacement reactions. We demonstrate how this process can direct the formation of specific metastable structures by design and that this dehybridization process can be controlled by DNA strand displacement reactions that effectively protect and deprotect a double-stranded complex from unwinding by Rep-X. These findings can guide the design of active DNA strand displacement regulatory networks, in which sustained dynamical behavior is fueled by helicase-regulated unwinding.

Branding the Earth: Selling Earth system science in the United States, 1983-1988

As part of its efforts to find new relevance in the early 1980s, NASA formed the Earth System Sciences Committee (ESSC) to develop a large-scale Earth science research program that would use satellites and computer modeling to study the planet as an integrated system with interconnections between the land, air, water, and biota. Called Earth system science (ESS), the project was conceived on the scale of the U.S. moon missions. Like the Apollo program, it would need enormous government funding to implement. Yet, the project was proposed just as government science funding was contracting. Conscious of the changing political economy of science, the ESSC attempted to build scientific, political, and public support for its project by using promotional techniques akin to the branding efforts more commonly identified in corporate marketing that were themselves changing in scope and importance in the 1980s. These techniques formed part of the ESSC's broader management strategy to promote ESS. The ESS brand was developed around the ideals of an interconnected 'Earth system', the significance of interdisciplinary research, and environmental concern. Though ESS failed to gain widespread traction, an unintended consequence of this branding was the communication and entrenchment of the concept of the 'Earth system'. Today, this concept provides crucial theoretical scaffolding that unifies interdisciplinary Earth science research, including climate change science.