Genome complexity: RNA protects from transposons (Introduction)

by David Turell , Tuesday, November 17, 2020, 19:18 (1250 days ago) @ David Turell

Found in plants:

https://phys.org/news/2020-11-rna-genome.html

"RNA is the intermediary nucleic acid that carries these instructions from DNA to ribosomes, where proteins are produced within the cell. But in humans and in plants, only a tiny fraction of DNA produces the RNA that carries out protein-building instructions. In humans, almost 98% of the genome does not encode proteins. However, it often gives rise to RNA that does not produce proteins, called noncoding RNA. So what does this portion of the genome do?

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"Now, research led by Wierzbicki shows that in plants, a portion of this noncoding RNA may play an essential role in protecting the integrity of the genome. This portion of noncoding RNA is produced from transposons, rogue pieces of genes that jump around within DNA, inserting themselves haphazardly and causing genetic diversity. Sometimes this diversity is beneficial, aiding evolution, says Wierzbicki, but sometimes it can trigger mutations that can lead to disease.

"The noncoding RNA produced from transposons is thought to protect the genome by making sure that transposable elements are permanently turned off. But how are transposons selected for silencing in the first place? In a recent study, the research team found evidence that this noncoding RNA is produced throughout the entire genome, not just at or around transposons.

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"With the polymerase enzyme mutated, the researchers then compared the mutated plant to a wild-type plant—a plant that had not been altered. If they detected RNA in the wild-type plant but not in the mutant plant, they could confirm that the noncoding RNA was real. And they did.

"Next, the researchers wanted to understand the role of this noncoding RNA. They expected to find that noncoding transcription was taking place on transposons, but nowhere else outside of the transposons. But what they found was that noncoding transcription was happening almost everywhere in the genome.

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"They found evidence that noncoding RNA is produced across almost 50% of the plant genome, while transposons composed only 10%-20% of the genome. By comparing their data to previously published results they further found evidence that this noncoding RNA is needed for silencing of transposons that became reactivated.

"'So when the transposon is new, or it has been activated in a way that the cell forgot it was previously marked as a foreign object, how can it be recognized as being foreign? Wierzbicki said. "There's one common factor that's always needed, and that's this noncoding RNA that we are studying. No matter where the transposon was inserted in the gene, it could not be turned off if the noncoding RNA was not present."

Comment: An amazing control process found in junk DNA. The exact role of jumping genes (transpons) is not known, but they are obviously active as described.