Biologist finds plant polymerases IV and V are really variants of Pol...( It's a little like finding out that ...),Health

It's a little like finding out that Superman is actually Clark Kent. A team of biologists at Washington University in St. Louis has discovered that two vital cellular components, nuclear RNA Polymerases IV and V (Pol IV and V), found only in plants, are actually specialized forms of RNA Polymerase II, an essential enzyme of all eukaryotic organisms, including humans.

"We've caught evolution in the act," said Craig Pikaard, Ph.D., Washington University professor of biology in Arts & Sciences. "We've known for decades that RNA Polymerases I, II and III are found in all eukaryotes, but it's only over the past several years that we've been aware that plants have two more nuclear polymerases, Pol IV and Pol V. Now it is clear that these enzymes evolved from Pol II over the past several hundred millions years. This is a new snapshot into the evolution of RNA polymerases, which are the enzymes responsible for decoding the information stored in the chromosomes".

Analyzing purified Pol IV and Pol V by a sophisticated technique known as tandem mass spectrometry, the Pikaard lab and a team of collaborators at Pacific Northwest National Laboratory, led by Ljiljana Paa-Toli?, discovered 12 subunits in both Pol IV and Pol V that correspond one-for-one to the 12 subunits of Pol II. Some of the Pol IV and Pol V subunits are encoded by the same genes as the corresponding Pol II subunits, but others come from duplicated Pol II subunit genes that have changed over time. Overall, four subunits of Pol IV are distinct from their Pol II counterparts, six subunits of Pol IV are different from their Pol II counterparts, and four subunits differ between Pol IV and Pol V. Yet, all of the Pol IV and Pol V subunits are "apples that haven't fallen far from the Pol II tree."

The finding is important because it reveals more about the roles played by RNA in complex organisms. RNA polymerases are the enzymes responsible for making R
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