Last year, this work converged with that of researchers investigating an extensive family of small molecules called microRNAs, or miRNAs, non-coding forms of RNA that appear to target and inactivate particular sets of messenger RNAs, thus preventing them from producing protein and effectively silencing the group of genes from which they were transcribed. In that study, Nishikura found that that precursor miRNAs, like messenger RNAs, are themselves subject to specific RNA editing, the result of which is to suppress ?or perhaps refocus ?miRNA expression and activity (http://www.nature.com/nsmb/journal/v13/n1/full/nsmb1041.html).
“MicroRNAs often target a specific set of genes,?Nishikura notes. “But when editing occurs, they may target a completely different set of genes.?
In recent years, Nishikura says, a growing number of scientists are discovering other links between RNA editing and the activities of different forms of non-coding RNA.
“We used to believe there were only a limited number of RNA editing sites,?she says, “but now we think there may be as many as 20,000 sites involving perhaps 3,000 genes. Interestingly, most of the editing sites correlate with non-coding regions of DNA, the so-called junk DNA.?
One reason for this, Nishikura and others speculate, may be that the majority of these non-coding regions are composed of repetitive sequences of DNA called transposons. The largest class of transposons, known as retrotransposons, have the remarkable ability to copy themselves into RNA, translate themselves back into DNA, and then reinsert themselves back into
Source:The Wistar Institute