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Biological Chemistry

In bacteria, gene transcription and translation are coupled

Researchers take a picture of the “expressome,” a bacterial megamachine composed of RNA polymerase and the ribosome

by Sarah Everts
April 17, 2017 | A version of this story appeared in Volume 95, Issue 16

Just when you thought the fundamental processes of gene transcription and translation could offer no more surprises, researchers report that RNA polymerase and the ribosome, the macromolecules responsible for transcription and translation, respectively, can be physically coupled in bacteria. The conjoined machinery was named the “expressome” by Patrick Cramer of the Max Planck Institute for Biophysical Chemistry, Robert Landick of the University of Wisconsin, Madison, and colleagues, who solved the 7.6-Å-resolution coupled structure using cryo-electron microscopy (Science 2017, DOI: 10.1126/science.aal3059). Textbooks worldwide describe the transcription of DNA into mRNA by RNA polymerase as a separate process from the subsequent translation of mRNA into a protein by the ribosome. Decades ago, scientists observed that “these two processes may be coupled in bacteria,” Cramer tells C&EN. But most scientists thought it was just the rates of the processes that might be coupled. “We show it is also a physical coupling,” Cramer adds. The expressome is unlikely to be found in multicellular creatures, such as humans, where transcription and translation occur in separate cellular compartments. But, Cramer adds that the expressome may be widespread in bacteria and Archaea, something he hopes the research community will further investigate.

Structure of the expressome.
Credit: Patrick Cramer/AAAS
Shown in these two views of the expressome, RNA polymerase (top) is coupled to the ribosome (bottom) in bacteria. The overall megamachine sequesters 30 mRNA nucleotides within.


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