Ayooshi Mitra, Amity University Kolkata
Transcription is a process that we often encounter while studying about gene expression. The transcription phase of gene expression allows the cells to live and do their jobs. We know that an enzyme called RNA polymerase wraps itself around the double helix of DNA during transcription. And using one strand to match nucleotides to produce a copy of genetic material, it results in a newly synthesised RNA strand that breaks down when the transcription is complete.
That RNA allows the production of protein, which is vital for all life and performs most of the work inside cells. RNA needs to start and stop in the proper place to make sense, just like any coherent message. Due to its ability to stop, or terminate, transcription, a bacterial protein called Rho was found more than 50 years ago. Rho is described in every textbook as a model terminator that binds to the RNA using its very strong motor force and pulls it out of the RNA polymerase. But a closer look by some researchers showed that Rho would not be able to find the RNAs as shown in the textbook mechanism.
New studies have identified and described a cellular process that has remained vague to scientists until now, despite what textbooks say, precisely how the copying of genetic material, once begun, is properly turned off. Thus for the first time, define how Rho protein really stops gene expression. The study revealed that Rho actually “hitchhikes” on RNA polymerase for the duration of transcription instead of attaching to a particular piece of RNA near the end of transcription and helping it unwind from DNA. It also showed how Rho cooperates with other proteins, in order to eventually fashion the enzyme through a series of structural changes that end with an inactive state allowing the RNA to be released.
Advanced microscopes were used to reveal how Rho operates on a complete transcription complex of RNA polymerase and two accessory proteins that travel throughout transcription with it. The expression of virulence genes in bacteria is known to silence Rho, essentially keeping them dormant until they are needed to cause infection. However these genes do not have any sequences of RNA that Rho is known to bind preferentially. As a result the researchers concluded how it never made sense for Rho to look only for specific RNA sequences, without even knowing if RNA polymerase is still attached to them. The researchers used cryo-electron microscopy in this study to capture RNA polymerase images functioning on a DNA template in their model system, Escherichia coli. Combined with high-end computation, this high-resolution visual representation made precise transcription termination modelling possible.
Also read: Moderna requests emergency authorization from FDA for mRNA – 1273
Reference:
Biology Textbooks Wrong? New Research Reveals the Secret Behind a Key Cellular Process, SciTech Daily, November 26, 2020, https://scitechdaily.com/biology-textbooks-wrong-new-research-reveals-the-secret-behind-a-key-cellular-process/
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