Light Fantastic Trips Gene Expression

Peter Quail and colleagues took advantage of the conformational properties of phytochrome, a chromoprotein that occurs naturally in plants. Phytochrome assumes two different shapes, Pr or Pfr, depending on whether it is exposed to red or far-red light. Only the Pfr form is capable of binding to another protein, PIF3. To exploit these properties to create a gene switch, Quail’s team engineered a yeast strain that produces two fusion proteins: one in which phytochrome is hooked onto a DNA-binding domain; and the other in which PIF3 is bound to a DNA-activation domain. Their idea was that gene expression would be induced only when the fusion proteins were in close proximity and binding upstream of the target gene. Sure enough, when they shone red light on the engineered yeast strain, the phytochrome in the first fusion protein changed from the Pr form to Pfr, which then was able to interact with PIF3 in the second fusion protein, bringing the DNA-binding domain and DNA activation domain together and inducing gene expression. Because of the reversible nature of the Pr/Pfr forms, Quail’s team could also turn off gene expression by placing the yeast in far red light and allowing the phytochrome to return to its natural Pr conformation, thus preventing the two fusion proteins from interacting.

The light triggered molecular switch has the advantage of allowing researchers to determine the function of a gene at different stages in a cell’s development, a benefit over other functional genomic methods, such as knockout technology. Also, the system is advantageous over other current molecular switches that need external chemical regulators because there are no uptake or toxicity problems.

Author contact:
Dr. Peter H. Quail
Dept of Plant and Microbial Biology
University of California, Berkeley, CA, USA
Tel: +1 510 559 5900
E-mail quail@nature.berkeley.edu

(C) Nature Biotechnology press release.

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