Monday, August 10, 2009

RNA Polymerase and Nucleosomes More Intricate Than Thought

In recent years new experimental techniques have been developed to analyze the actions of single molecules, rather than populations of molecules. Such techniques have been useful in researching large molecules that act alone, such as RNA polymerase--the massive molecular machine that makes copies of the long DNA strands in our cells. A new study now shows some of the intricacies of how RNA polymerase works its magic.

One of the complications that RNA polymerase faces is that its target DNA strands are sometimes tightly compressed. In fact, if all the DNA in your body was stretched out it would reach to the moon and back many thousands of times. Part of the DNA compaction is achieved by winding it around small proteins called histones. The DNA wraps around a bundle of eight histones forming what is called a nucleosome.

On a side note, histones show a high degree of similarity between species. The histone IV protein, in particular, shows only a few changes between different species. Not surprisingly, evolutionists predicted that there must be a strong functional constraint on histone sequences, allowing for only a few mutations in these gene sequences. But experiments showed otherwise. Significant mutations in the histone sequences in yeast cells made less difference than expected.

So how does RNA polymerase make a copy of the DNA strand if, at repeated intervals, the strand is wrapped around a histone octamer? Not surprisingly evolutionists imagined a rather simple explanation: the RNA polymerase must simply bulldoze its way through the nucleosome. And not surprisingly that view is false.

The new research suggests a more nuanced approach. As one of the researchers put it, the polymerase is "surprisingly delicate in its response." The polymerase actually backs up a bit while the DNA may unwrap, for instance. And the researchers discovered that the tension in the DNA strand may play an important role in influencing the polymerase-nucleosome interaction. As another researcher concluded:

These experiments give a much more dynamic picture of the nucleosome, showing that it isn't a static bead-on-a-string but an active structure that can regulate when and how our genetic information is read.

Why is it that biology always seems to be more complicated than evolution had envisioned it to be?