The inside story
FROM being the ultimate tool of bakers and those in the brewery industry to the prolonged cynosure of geneticists, the humble yeast has come a long way. Its similarity to the human cell has allowed scientists to arrive at a breakthrough which is being variously described as a "triumph" and "milestone" ; they have at long last deciphered the complete genetic blueprint of the yeast cell. The happy tidings were announced at two news conferences held simultaneously, one at the National Institutes of Health in the us and the other in Brussels on April 24.
What the achievement, covering many human-hours of tedious work and involving a number of nations, across a span of seven years, holds is mammotb. The encoding of the yeast's genetic layout could primarily aid a quick response to all that ails humankind and to find antidotes to combat them. For, as Mark Johnston of the Washington University in St Louis, one of the centres that took part in the research, puts it, "virtually all of the genes in yeast are also in humans". So, if a gene which causes any disease in humans,' say breast cancer or Huntington's disease is found, then the same can be checked in the yeast cell, to see if there is a counterpart gene in it too. And if it exists, then it becomes all the more easier to observe the gene's function in the yeast to arrive at its human role.
The odyssey to discover the genetic outline of the yeast cell began in 1989 at the behest of Andre Goffeau, a biochemist at the Catholic University of Louvian-la-Neuve in Belgium. Initially a project divided among European laboratories, it soon had the us and Japan joining it. Laboratories numbering over 70 were invested with the responsibility of determining the sequence of nucleotides, or the DNA building blocks. The findings were then entered into a computer database which could be accessed by scientists anywhere in the world. Over 6,000 genes of the yeast with 12 million nucleotides are now within the purview of geneticists.
.. While scientists have yet to detail the functions of all the genes, they have discovered the basic purpose of most of them - regulating the activity of other genes. The other important chore of the yeast gene is to create such substances that will in turn set off internal activity within the genes. According to Ron Davis, a geneticist from Stanford University, many genetic controls in yeast coincide with those in the humans. For example, the division of a single yeast cell to yield two is similar to the human cell reproduction.
So far, scientists have encoded the genetic blueprint of some viruses and two species of bacteria, but these pale into insignificance on account of their primitive nature. In contrast, the finding of the genetic code of the yeast will encompass the larger framework of getting closer to the human genetic map. Already, yeast is being used to get to the root of genetic diseases like hereditary colon cancer and neurofibromatosis, a disorder that leads to the growth of tumours along the nerves. Another important factor of the yeast's genetic code is the advantage it poses to treating human disorders. Drug trials can now be performed in yeasts to note their reaction and can help in accelerating medical improvements. While tests on mice may take several years to achieve results, it is much faster using the yeast cell considering its single-cell status.
This is only the beginning. Flushed with their success with the yeast, scientists have set up some stiff targets for themselves in the coming years. For starters, they will get to cracking the genome of a little worm called Caernorhabditis elegans which is to be completed by 1998. The C elegans' code should be of interest as it involves the bio-chemistry of aging. Further, many a tropical disease is worm-borne and the availability of genetic data of the worm could help in pinpointing the method to contain its spread.
By next century, the human gene story will also be told, replete with details of the 100,000 genes on the 46 chromosomes, entailing nearly three billion nucleotides. The Human Genome Project, as it is known, first began with learning more of the diseases which are hereditary in nature. It has now culminated into a us $3 billion worldwide project. Apparently, nearly 4,000 genes could be the culprits behind inherited diseases. Further, geneticists also believe that deadly diseases like cancer and heart disease could be genetically inherited.
Yet another venture of these top brains would be to have a go at revealing the genetic network of the Arabidopsis or the thalecress weed. This weed grows in abundance on a wide geographic range, from the north of Sweden to the Cape Verde islands off the west coast of Africa. The weed is similar to important crop plants and its gene code could help in preventing crop diseases.
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