Evolution of Genetic Storage

In each human cell there is about 2m of genetic material packaged into our chromosomes. In order to fit such a large amount of genetic material into a cell, double-stranded human DNA is tightly wound using histones. Recently though, researchers at the University of Chicago discovered that single-celled aquatic algae called dinoflagellate have evolved an alternate way of packaging their DNA.

Packing of DNA is a difficult task due to the negative charge on the phosphate atom which must be neutralised to overcome electrostatic repulsion. Dinoflagellates have considerably more nuclear DNA that humans. In humans, positively-charged histone proteins bind DNA into nucleosomes. Dinoflagellates however, contain no histones or nucleosomes. So how do they condense their DNA into packages?

By using a high resolution scanning microprobe, researchers found that dinoflagellates had calcium and magnesium cations embedded in their DNA. This, in addition to the discovery that removal of calcium and magnesium cations caused an explosion of dinoflagellate chromosomes strongly suggested that these cations played a cricial role in the packing of DNA.

This leads to the question of how such evolution occurred in the first place. Did dinoflagellates initially have histones and over time, lost them? Or is this simply a case of convergent evolution, where alternate methods have evolved to perform the same function?

References:
- http://www.physorg.com/news138540908.html

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