Breakthrough Research, S. cerevisiae
Life With 6000 Genes
By the late 1990's, through an international collaboration of over 600 scientists, Saccharomyces cerevisiae became the first eukaryote with a completely sequenced genome. The paper, Life with 6000 Genes published in Science in 1996 documents the process, findings and overall implications of this genome project that helped shaped our knowledge of S. cerevisiae into what it is today.
5885 protein encoding genes have been identified through the genome project and have revealed a remarkable compact organization of genes compared to other yeasts and fungi. This is largely due to the lower instance of introns in S. cerevisiae which accounts for less interruption of genes. S. cerevisiae was found to have less than 4% of it's nearly 6000 genes to contain introns compared to fellow yeast Schizosaccharomyces pombe which has introns in 40% of its genes.
Now that the entire genome has been sequenced the process of identifying the function of each gene can come underway. The S. cerevisiae genome project has paved the way for other eukaryote genome sequencing projects, particularly those which have industrial or medical significance like S. pombe and C. elegans.
5885 protein encoding genes have been identified through the genome project and have revealed a remarkable compact organization of genes compared to other yeasts and fungi. This is largely due to the lower instance of introns in S. cerevisiae which accounts for less interruption of genes. S. cerevisiae was found to have less than 4% of it's nearly 6000 genes to contain introns compared to fellow yeast Schizosaccharomyces pombe which has introns in 40% of its genes.
Now that the entire genome has been sequenced the process of identifying the function of each gene can come underway. The S. cerevisiae genome project has paved the way for other eukaryote genome sequencing projects, particularly those which have industrial or medical significance like S. pombe and C. elegans.
Leeland Hartwell, Yeast and Cancer
One of the most important experiments performed with S cerevisiae was one that was done by the geneticist Dr. Lee Hartwell. He wanted to find an organism that was going to be easy to manipulate but complex enough for the cells to resemble human cells. As he went further into his research he decided that he wanted to focus on the cell cycle and the reasons why some cells wouldn’t stop dividing. S cerevisiae was perfect to use since it is a single celled eukaryote and follows the same cell cycle as human cells with G1,G2,S and M phases. Another primary reason for choosing S cerevisiae to work with was that as its cells progress through the cell cycle it was easy to identify the morphological changes that its cells were undergoing. Photo microscopy was useful since having a small bud identifies the cells that are at the beginning of the cell cycle. After knowing what a normal cell cycle encompasses it was possible to determine any mutants that had defects in the cell cycle.
Dr Lee Hartwell and his team were able to identify more than one hundred genes that were involved in the control of the cell cycle. By knowing what genes are involved in the cell cycle it became easy to determine any mutants that were present. These mutants allowed for further analysis of the cell cycle pathway and what regulation events were occurring. This was done by how far the cell cycle progressed before stopping the cycle completely. By analyzing these events their results showed that mutants had primary defects in each of the events happening in the cell cycle. As the cells were in arrested development they would eventually produce a terminal phenotype, which was dependent on the event that was occurring. The event that happened first was controlled by the CDC28 gene and was required to be completed prior to the start up of any proceeding pathways. The next two pathways were ones that led to budding, nuclear migration, cytokinesis etc. This meant there were a series of dependent events which required completion before moving along the pathway. Cells consistently receive signals from the environment and can either stimulate or inhibit the cell division. If these genes are not capable of regulating their checkpoints then it leads to uncontrolled cell growth or the proliferation of tumors. These checkpoints act in a major way to fix any problems that the cell may having during division. Without the use of these simple organisms it wouldn’t have been possible to better understand the human cell division cycle.
Lee Hartwell was awarded the Nobel Prize in 2001 in Physiology and Medicine for his research on yeast and cancer. His Nobel lecture speech published in Bioscience Reports can be found in the Links section of this site.
Dr Lee Hartwell and his team were able to identify more than one hundred genes that were involved in the control of the cell cycle. By knowing what genes are involved in the cell cycle it became easy to determine any mutants that were present. These mutants allowed for further analysis of the cell cycle pathway and what regulation events were occurring. This was done by how far the cell cycle progressed before stopping the cycle completely. By analyzing these events their results showed that mutants had primary defects in each of the events happening in the cell cycle. As the cells were in arrested development they would eventually produce a terminal phenotype, which was dependent on the event that was occurring. The event that happened first was controlled by the CDC28 gene and was required to be completed prior to the start up of any proceeding pathways. The next two pathways were ones that led to budding, nuclear migration, cytokinesis etc. This meant there were a series of dependent events which required completion before moving along the pathway. Cells consistently receive signals from the environment and can either stimulate or inhibit the cell division. If these genes are not capable of regulating their checkpoints then it leads to uncontrolled cell growth or the proliferation of tumors. These checkpoints act in a major way to fix any problems that the cell may having during division. Without the use of these simple organisms it wouldn’t have been possible to better understand the human cell division cycle.
Lee Hartwell was awarded the Nobel Prize in 2001 in Physiology and Medicine for his research on yeast and cancer. His Nobel lecture speech published in Bioscience Reports can be found in the Links section of this site.