Does DNA in the cell nucleus remain stationary while RNA molecules, responsible for transcribing genes, move around it? It turns out to be the other way around! Instead, DNA itself is in motion. This is the only way to prevent entanglement within the nucleus, as demonstrated by a Polish-British team of scientists.
DNA resembles a long scroll of papyrus containing instructions for proteins and RNA. To extract information from it, a special “reader”—RNA polymerase—must travel along its length, decoding the information and automatically generating an ever-growing, thread-like receipt—RNA, which serves as the blueprint for protein synthesis.
Until now, it was commonly imagined that RNA polymerases, the molecular engines responsible for transcription, moved along a stationary DNA strand. However, at any given moment, there are tens of thousands of these readers within the nucleus, and a particularly important gene may be read simultaneously by several dozen polymerases.
Yet, as we have known since the discoveries of Franklin, Watson, and Crick, DNA consists of a twisted double helix. Do these readers orbit the DNA strand while pulling along their ever-lengthening RNA transcripts, sometimes extending up to several thousand nucleotides? If that were the case, every newly synthesized RNA molecule would need to rotate at a speed of four revolutions per second. That scenario seems implausible!
Anyone who has ever dealt with a bag full of unused cables knows how easily long, thin elements can become tangled and how much energy is required to untangle them later. A bit of imagination is enough to understand that the model of polymerases running along the DNA strand does not make sense. Nature must have devised a smarter solution.
Now, thanks to new research published in Cell Reports, we should update our understanding of what happens inside every nucleated living cell on Earth. “Gene expression inherently involves rotation. We demonstrate that it is the DNA that rotates, driven by the simultaneous action of molecular motors responsible for transcription. It would make no sense for these motors to rotate themselves,” explains Dr. Tomasz Turowski, head of the Transcription Mechanisms Laboratory at the Institute of Biochemistry and Biophysics of the Polish Academy of Sciences, in an interview with PAP.
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The Simplest Version of the Model
Consider a circular clothing rack in a store. You could walk around it to browse the garments, or you could stand still and rotate the rack like a carousel, bringing each item into view. The latter strategy works particularly well when multiple people are browsing simultaneously, as the continuous rotation eliminates the need to push through crowds. Instead, the shoppers simply coordinate their browsing speed with one another.
The Polish-British research team has provided evidence that the rotation of DNA arises from the synchronization of RNA polymerases. Dr. Turowski explains that DNA rotation integrates the actions of multiple polymerases into a coordinated convoy, allowing them to work together efficiently.
The RNA molecules being produced serve as anchors, holding the polymerases in place. Models show that if these RNA anchors are cut, DNA rotation slows down. “Traditionally, RNA polymerases were thought to function independently, but our latest research reveals that on ribosomal DNA (rDNA) genes, their actions are synchronized through rotational coupling of the DNA. This introduces a new way of thinking about gene expression,” Dr. Turowski describes.
A New Perspective on Quality Control in Gene Expression
When this synchronized convoy halts, precise cleavage of the newly formed RNA triggers pausing and backtracking of the polymerases, which is crucial for ensuring the quality of the produced RNA molecules. Additionally, defective or stalled RNA fragments are tagged with a short sequence, enabling their removal by cellular repair systems.
Previously, it was assumed that protein synthesis and quality control processes occurred sequentially. However, this new discovery reveals that these processes can directly influence each other.
Ludwika Tomala (PAP)
Science in Poland
Full article (Polish): A jednak się kręci! DNA obraca się dzięki wspólnej pracy komórkowych silniczków | Nauka w Polsce
