Prions speed evolution
Helen Pearson

Sloppy proteins may help organisms adapt.

Prions, the twisted proteins usually linked to disease, could help organisms
adapt to tough situations by subtly altering the proteins manufactured by a
cell. The discovery backs the idea that proteins as well as DNA are vital in
driving evolution.

Prions are proteins that twist into one of two shapes. In mammals, one type
of prion seems to be harmless in one form but is infectious in the other. It
is thought to underlie mad cow disease and its human equivalent, variant
Creutzfeldt-Jakob disease (vCJD).

But scientists studying yeast (Saccharomyces cerevisiae) have found that, in
some cases, infectious prions may have an important role. In a colony of
yeast cells, some cells carry the 'normal' type of the protein, whereas
others harbour the infectious form, which accumulates into clumps and is
passed from one cell to another.

Four years ago, Susan Lindquist and Heather True of the Whitehead Institute
in Cambridge, Massachusetts, showed that this yeast prion can change the way
that cells behave. In their infectious form, the prions sometimes helped the
yeast to adapt, changing their rates of survival when they were grown in
various nutrients or temperatures.

Now Lindquist and her colleagues have worked out how the prions do this. In
its non-infectious form, the protein normally helps to read and convert the
DNA code into other proteins. But in its infectious form, the prion stops
working. This means that many proteins are manufactured slightly sloppily.

Read the rest at Nature
http://www.nature.com/news/2004/040816/full/040816-1.html

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