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Posted on 03/03/2013 12:36:32 AM PST by neverdem

RNA ‘sponges’ mop up sequences that curb gene expression.

Behold the latest curio in the cabinet of RNA oddities: naturally occurring circular RNA molecules that influence gene expression.

At least some of the loops, described in two papers published this week by Nature1, 2, act as molecular ‘sponges’, binding to and blocking tiny gene modulators called microRNAs. But the researchers suspect that the circular RNAs have many other functions. The molecules comprise “a hidden, parallel universe” of unexplored RNAs, says Nikolaus Rajewsky, the lead author of one of the studies and a systems biologist at the Max Delbrück Center for Molecular Medicine in Berlin.

The discovery is yet another a reminder that RNA is much more than a mundane messenger ­between DNA and the proteins it encodes. The past two decades have seen the discovery of a host of nonconformist RNAs. Some were unexpectedly short or surprisingly long, and some flouted orthodoxy by blocking other RNA strands from being translated into protein. But almost all were linear. The few accounts of circular RNAs in plants and animals were generally dismissed as genetic accidents or experimental artefacts, says Erik Sontheimer, a molecular biologist at Northwestern University in Evanston, Illinois.

Instead, the predominance of linear RNAs may have been the artefact. Typical RNA-sequencing methods isolate only those mol­ecules with characteristic molecular ‘tails’. With their ends joined together, round RNAs lack those tails, so have generally been overlooked.

But advances in sequencing have allowed biologists to accumulate large data sets of RNA sequences, including some from RNA without tails. Last year, Julia Salzman, a molecular biologist at Stanford University School of Medicine in California, and her colleagues sent the first missive from the circular universe. They reported finding a plethora of circular human RNAs while searching for RNA molecules that conventional methods might...

(Excerpt) Read more at nature.com ...

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Thanks neverdem. [snip] "For thirty years, nobody disputed this 'fact'. One group of scientists abandoned their experiments on human liver cells because they could only find twenty-three pairs of chromosomes in each cell. Another researcher invented a method of separating the chromosomes, but still he thought he saw twenty-four pairs. It was not until 1955, when an Indonesian named Joe-Hin Tjio travelled from Spain to Sweden to work with Albert Levan, that the truth dawned. Tjio and Levan, using better techniques, plainly saw twenty-three pairs. They even went back and counted twenty-three pairs in photographs in books where the caption stated that there were twenty-four pairs. There are none so blind as do not wish to see." [/snip] -- Matt Ridley, Genome: The Autobiography of a Species in 23 Chapters (p 23-24) James D. Watson and Francis Crick discovered the structure of DNA in 1953 -- two years earlier. Just adding to the catalog, not sending a general distribution. To all -- please ping me to other topics which are appropriate for the GGG list.

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