Schizosaccharomyces pombe

Schizosaccharomyces pombe, also called "fission yeast", is a species of yeast. It is used as a model organism in molecular and cell biology. It is a unicellular eukaryote, whose cells are rod-shaped. Cells typically measure 3 to 4 micrometres in diameter and 7 to 14 micrometres in length. It is also possibly the eukaryote with the shortest genome (about 13.8 million base pairs).

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These cells maintain their shape by growing exclusively through the cell tips and divide by medial fission to produce two daughter cells of equal sizes, which makes them a powerful tool in cell cycle research. Such research is critical as it is important to understand how cells grow and differentiate as well as how non-controlled growth results in cancerous cells.

Fission yeast was isolated in 1893 by Lindner from East African millet beer. The species name is derived from the Swahili word for beer (Pombe). It was first developed as an experimental model for studying the cell cycle by Murdoch Mitchison in the 1950s.

The fission yeast researcher Paul Nurse, together with Lee Hartwell and Tim Hunt, won the 2001 Nobel Prize in Physiology or Medicine, for their work on cell cycle regulation.

The sequence of the S.pombe genome was published in 2002, by a consortium led by the Sanger Institute, becoming the sixth model eukaryotic organism whose genome has been fully sequenced. This has fully unlocked the power of this organism, with many genes homologous to human disease genes, including diabetes and cystic fibrosis, being identified.

In 2006, sub-cellular localization of all the proteins in S. pombe was published using the green fluorescent protein as a molecular tag.

S.pombe has also proved to be an important organisim for unlocking the secrets of the cell cycle response to DNA damage and DNA replication.

Comparison with budding yeast or Saccharomyces cerevisiae

• S. cerevisiae has ~ 5600 open reading frames, Sch. pombe has ~ 4800 open reading frames
• S. cerevisiae has 16 chromosomes, Sch. pombe has 3
• S. cerevisiae is usually diploid while Sch. pombe is usually haploid
• S. cerevisiae is mainly in G1 state (consequently G1-S transition is tightly controlled) while Sch. pombe is usually in G2 state (consequently G2-M transition is under tight control)
• Both species share genes with humans that they do not share with each other . Sch. pombe contains the same heterochromatin genes as humans; they are missing from S. cerevisiae. Conversely, S. cerevisiae has well developed peroxisomes; Sch. pombe does not.
• S. cerevisiae has small point centromeres of about 100bp, and sequence-defined replication origins around the same size. Conversely, Sch. pombe has large, repetitive centromeres (40-100kb), and degenerate origins of at least 1kb.
• S. cerevisiae has no RNAi pathway while Sch. pombe does.