Birth of an miRNA

The paper:

The finding:

Bryan Cullen and colleagues at Duke University and the University of Kansas investigated the development of human micro-RNAs (miRNAs) to find that their precursors, primary miRNAs (pri-miRNAs), aren?t that different from protein coding mRNAs. Looking at nine of these pri-miRNAs they found poly adenylated tails and 5' caps, and evidence suggests that they?re transcribed by RNA polymerase II.

The surprise:

One of the subjects, miR-21, which is 22 nucleotides long, is processed out of a primary transcript more than 3,400 nucleotides long and intronless. ?People weren?t thinking in terms of long transcripts turning into small ones, says Cullen. The precursor to miR-21 even proved able to produce functional mRNA in transfected cells.

The significance:

John McCarthy, a geneticist at the University of Kentucky, says the work is likely highly cited because ?it provides a framework for how miRNAs are generated and how they themselves may be regulated.?

The next step:

?We have over 400 different miRNAs in the human genome,? says Cullen. In addition to tracking the rest down, Cullen has been looking into viral miRNA expression. ?If you can interfere with miRNAs you might be able to stop infection,? says Cullen.