ScienceDaily (Jan. 15, 2008) – MIT scientists have found a new way that DNA can carry out its work that is about as surprising as discovering that a mold used to cast a metal tool can also serve as a tool itself, with two complementary shapes each showing distinct functional roles.

Professor Manolis Kellis and postdoctoral research fellow Alexander Stark report in the Jan. 1 issue of the journal Genes & Development that in certain DNA sequences, both strands of a DNA segment can perform useful functions, each encoding a distinct molecule that helps control cell functions…

The surprising discovery is that for some microRNA genes, both DNA strands, instead of just one, encode RNA, and both resulting microRNAs fold into hairpins that are processed into mature microRNAs. In other words, both the tool and its mold appear to be functional. Kellis and Stark found two such microRNA pairs in the fruit fly, and eight more such pairs in the mouse.

The idea that there could be such dual-function strands, where both DNA strands encode functional RNA products, “had never even been hypothesized,” Kellis says. But follow-up work confirmed that they did indeed function in this way. The work suggests that other such unexpected pairings, with both DNA strands encoding important functions, may also exist in a variety of species.

This discovery builds on a similar, earlier surprising finding about microRNA regulation. In December, Stark and Kellis reported that both arms of a single microRNA hairpin can also produce distinct, functional microRNAs, with distinct targets. Together, these two findings suggest that a single gene can encode as many as four different functions–one hairpin from each of the two DNA strands, and then one microRNA from each of the two arms of each hairpin…

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