IN A TWIST: Certain guanine-rich regions of the transcriptome can fold up into four-stranded structures called RNA G-quadruplexes that are thought to have harmful effects in living cells. Both eukaryotes and bacteria have evolved mechanisms to keep these structures unfolded, according to a new study. Eukaryotes likely have protein machinery—possibly helicases to unravel the structure (1) and proteins that bind to the transcripts to keep them from reforming (2). Bacteria appear to have depleted quadruplex-forming sequences from their genomes during their evolution.© KIMBERLY BATTISTA
The paper
J.U. Guo, D.P. Bartel, “RNA G-quadruplexes are globally unfolded in eukaryotic cells and depleted in bacteria,” Science, doi:10.1126/science.aaf5371, 2016.
RNA doesn’t lie flat. Interactions between nucleotides can turn sections of transcripts into loops, bends, and knots, some of which have regulatory functions in the cell. It was with these tangles in mind that Junjie Guo, a postdoc in David Bartel’s lab at MIT, developed an in vitro chemical probe to detect folded regions of RNA. “We were trying to identify all the structures that can stably form in vitro,” he says.
Testing the technique on transcripts extracted from mouse embryonic stem cells, Guo found that one particular conformation was unexpectedly abundant: RNA G-quadruplexes—stable, guanine-rich regions folded into four-stranded structures. “Only dozens of [these] ...
