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What is an EST?
An EST, or "expressed sequence tag," is a DNA sequence of several hundred nucleotides. As the name implies, an EST is DNA that codes for a particular protein. ESTs are DNAs that have been transcribed and are ready to be translated into a protein. An EST is typically obtained by determining the sequence of several hundred nucleotides of one end of a gene. Because several hundred nucleotides are more than sufficient to distinguish any given gene from all other genes, an EST is a convenient means of identifying a specific gene in the context of a single chromosome, a complete genome or a collection of genes (often called a "library").
EST Uses
ESTs have a number of immediately useful characteristics. For example, an EST can be used as a label to map a specific location on a chromosome. Because the sequence information contained in an EST is enough to distinguish one gene from all others, each EST may be used to identify the chromosomal location of its corresponding gene. The ability to identify where a particular gene is on the chromosome is important in the detection of chromosomal mutations and corresponding disease states. Using an EST as a tool in this way may allow a doctor to diagnose a particular genetic disease in time to provide a preventive treatment.
ESTs may also be used to distinguish between cell or tissue types. Although nearly all cells and tissues of a given organism contain all the genes of that organism, each cell or tissue type typically expresses, or manufactures, the proteins encoded by only a subset of genes (for example, a gene involved in vision may be expressed by a retinal cell, but not expressed by a muscle cell). Thus, because each EST corresponds only to a single expressed gene, a scientist or doctor may use an EST to identify a cell or tissue by which gene or genes are expressed or not expressed. In a similar way, ESTs may also be used as molecular tools in criminal investigations.
EST Patents
Currently, many patent applications directed to ESTs are pending before the U.S. Patent and Trademark Office. The PTO has adopted the policy that an EST may be patented if it meets the utility, novelty and the nonobviousness requirements.
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