Sunday, November 27, 2005

Watching DNA transcription

DNA is a really long molecule -- almost arbitrarily long, in fact. A single strand of human DNA can be as long as 5 cm. But it's also very narrow, about 2 nm (2×10-7 cm). Further, the distance between each base pair that makes up the molecule is only .34 nm. It's hard to imagine actually being able to see directly what's going on as DNA is transcribed into RNA in the first step of the process which eventually makes a protein molecule.

But that is exactly what has recently been accomplished, and it answers an obvious question: Does the RNA polymerase enzyme which transcribes DNA into RNA work by translating a single base unit at a time, or does it operate in batches of several base units? It seems that we now have the answer:

Ultra-sensitive microscope reveals DNA processes
“For years, people have known that RNA is made up one base at a time,” Block [researcher who co-designed the experimental equipment] says. “But that has left open the question of whether the RNAP enzyme actually climbs up the DNA ladder one rung at a time, or does it move instead in chunks – for example, does it add three bases, then jump along and add another three bases.

And the answer is?
“The RNAP climbs the DNA ladder one base pair at a time – that is probably the right answer,” he says.



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