MicroRNAs, noncoding RNAs widely thought to repress gene expression, can also perform the opposite role of activating translation, according to a study published online today in Science.The study "makes us rethink how microRNA regulates genes," said Phillip Sharp of the Massachusetts Institute of Technology, who was not a coauthor. "By current dogma, all regulation is thought to be negative -- in cancer, immune responses, everything. This is not a small issue, and it's going to be debated."MicroRNAs exert their effects by targeting messenger RNA, and, most researchers hold, repressing protein translation. However, a few previous studies have raised the possibility that microRNAs play an activating role, said Shobha Vasudevan of the Yale University School of Medicine, the lead author of the paper. One study reported that a microRNA found in the human liver increased replication of RNA of the Hepatitis C virus (HCV), presumably by...

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