New genome sequence information from the humble baker's yeast has revealed surprising variation in a set of genes that can be thought of as nature's oldest clock. In a paper published in Genome Research scientists show how ribosomal RNA genes that are essential to all Earth's organisms provide insight into how genomes maintain their integrity on their evolutionary journey.



Ribosomal RNA sequence changes have been ticking away like clockwork for over 3 billion years, maybe even pre-dating the origin of the DNA world itself. However, even the slightest changes in sequence of these genes can be fatal. It is vital to conserve the important genetic 'cogs' to make sure cells function correctly. However, significant changes do occur, contrary to expectation, and yet the yeast somehow still survives.

Furthermore, when two yeasts hybridize the clocks appear to re-set, apparently overwriting each others' rhythm and eliminating unwanted variations on the theme. This provides clues as to how key motifs are conserved and allows us to track the evolutionary history of hybrids.

Steve James, lead researcher at the Institute of Food Research (IFR), said "I have sequenced these genes to selectively identify yeast species for over 15 years and had no idea they would turn out to be so variable."

Rob Davey, computational biologist at the National Collection of Yeast Cultures (NCYC), said "we can use new computer techniques to model the changes mathematically and really get to grips with what orchestrates the variation in these important cell housekeepers."

Ian Roberts, Curator of NCYC, said "Yeasts are everywhere around us in nature and industry. This extra level of detail allows us to resolve important differences between yeasts and gain maximum benefits from their use in food, drink and healthcare."

Yeast production is a multi-billion dollar industry for brewing, baking, biofuel production, probiotics, and medical applications. The strains used in this study are publicly available alongside several thousand other yeasts at www.ncyc.co.uk. The collection is supported at the IFR by the BBSRC and seeks to make yeast strains and knowledge available to industrial and academic scientists in an equitable and efficient manner.

his research was funded by the BBSRC, the Wellcome Trust, NSF, NIH and the Hertz Foundation. This work was carried out in collaboration with the Wellcome Trust Sanger Institute and the Massachusetts Institute of Technology. The IFR is an institute of the Biotechnology and Biological Sciences Research Council (BBSRC).

Article: "Repetitive sequence variation and dynamics in the ribosomal DNA array of Saccharomyces cerevisiae as revealed by whole-genome resequencing" Genome Res. 2009. 19: 626-635