Scientists discover small RNAs that regulate gene expression and protect ...(gulators. A New Class of RNA P...)

Previously, researchers had recognized two classes of regulatory small RNA molecules in fruit flies, each with different protein partners. One class, called microRNAs, appears throughout the organism and acts to regulate the activity of many genes by joining with a special protein called Argonaute 1. A second class of RNA molecules, called piRNAs, occurs only in cells of the sex organs, and joins with different proteins, called Piwi proteins. Together, they act as a kind of immune system to suppress genetic interlopers called transposable elements, which were discovered at CSHL by Nobel laureate Barbara McClintock more than a half century ago, and which in certain cases can cause genomic havoc that underlies disease.

Dr. Hannon and his colleagues looked for RNA molecules that partner with a different protein, Argonaute 2, that belongs to the same family as Argonaute 1 and the Piwi proteins. Using advanced sequencing technology, they found that these small-RNA partners were distinct from either of the previously known classes of small RNAs. The new small-RNA class both modifies gene activity and suppresses transposable elements, thus serving as a defense mechanism.

These findings, the scientists write in a newly published paper in Nature, expands the known repertoire of small RNAs in fruit flies, and further blurs distinctions between the previously identified classes of small RNAs.

In related research, Hannon and his colleagues have published a paper announcing their discovery of a new source of regulatory RNA in mice. Many RNA sequences, such as microRNAs, are flagged as regulatory molecules because they physically fold on themselves. Special proteins recognize the resulting double-stranded RNA, and chemically slice it to release regulatory RNA snippets.

The CSHL team found that double-stranded structures also form from pseudogenes.
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