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Schizosaccharomyces pombe: Second yeast genome sequenced
By Birgit Reinert


An international group of researchers has sequenced the genome of the fission yeast Schizosaccharomyces pombe. The single-celled fungus was first isolated from East African millet beer more than a century ago, and the second part of its name stems from the Swahili word pombe for beer.

The fission yeast Schizosaccharomyces pombe.

The researchers identified fifty genes of S. pombe associated with human diseases—including cystic fibrosis, hereditary deafness, and diabetes. "The largest group of human disease-related genes are those implicated in cancer," the researchers write in Nature. "There are 23 such genes, and they are involved in DNA damage and repair, checkpoint controls, and the cell cycle, all processes involved in maintaining genomic stability."

"Significantly, many decisions the humble yeast cell makes in cell division use genes that are closely related to genes implicated in many human cancers," Paul Nurse of the Cancer Research UK in London is quoted as saying. The findings are expected to help better understand the basic biology behind cancer and how cancer and other human diseases develop.

The fission yeast is the sixth organism with a nucleus to have its genome sequenced, following humans, the nematode worm, the fruit fly, mustard weed, and budding yeast.

Of these completed eukaryotic organisms, S. pombe has the smallest and most compact genome. It contains 13.8 million base pairs distributed among three chromosomes and 4,824 genes. This is the lowest number of protein-coding genes yet identified in a free-living eukaryotic cell. It is also substantially lower than the 5,600 genes found in S. pombe's cousin, the other yeast Saccharomyces cerevisiae, whose genome was mapped in 1997.

A comparison between the fission yeast and the budding yeast—the only two single-celled organisms among the six—revealed similarities and differences between the two: Only two genes are unique to S. pombe that have relevance to human disease. On the other hand, the researchers also identified several hundred genes and proteins in S. pombe that do not appear in S. cerevisiae. This makes both species complimentary model organisms for studying eukaryotes.

The findings will also allow researchers to find out more about the evolution of one-celled and multi-celled eukaryotic organisms compared to others such as bacteria, which do not have nucleated cells. Further analyses and comparisons should reveal which genes define eukaryotic cells and the transition from one-celled to multi-celled organisms.

"In all these comparisons, it will be important to go beyond simply identifying the similarities and differences between species, and to analyse the origin of the differences, for example the gain, loss and possible transfer of genes over time," writes Jonathan A. Eisen of The Institute for Genomic Research in Rockville, Maryland in an accompanying News and Views article.

The sequencing of S. pombe involved more than one hundred researchers from laboratories around the world. The international project was led by Nurse who recently was among the winners of the 2001 Nobel Prize in Physiology or Medicine for his research on the cell cycle in fission yeast.

This month, scientists from all over the world working on S. pombe will come together in Kyoto, Japan at The 2nd International Fission Yeast Meeting (POMBE 2002), March 25-30, 2002.

Data on the S. pombe sequencing project is available online at the British Wellcome Trust Sanger Institute

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Eisen, J.A. Genome sequencing: Brouhaha over the other yeast. Nature 415, 845-848 (February 21, 2002).
Wood, V. et al. The genome sequence of Schizosaccharomyces pombe. Nature 415, 871-880 (February 21, 2002).

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