Expressed Sequence Tags

	Expressed Sequence Tags Download this lecture Now a days, genome analysis has employed a rapid analysis tool known as Expressed Sequence Tags. In 1983, SD Putney for the first time demonstrated the use of cDNA in identification of genome. The term Expressed Sequence Tags (ESTs) was coined by Anthony Kerlavage at the Institute for Genomic Research . In 1991, Mark Adams used EST in relation to gene discovery and Human Genome project. _____________________________________________________________________ cDNA or complementary DNA is reversely transcribed from mRNA using reverse transcriptase enzyme. cDNA is widely used in cloning of genes in eukaryotes. -------------------------------------------------------------------------------- Expressed Sequence Tags or ESTs , as the name suggests, are the new generation tools providing new dimension to transcriptome analysis. They are the tiny sequences of cistron randomly selected from genome library and can be used to identify and map the whole genome of any particular species. ESTs are usually 200 to 500 nucleotides long and are generated by sequencing the ends of DNA. ESTs can be obtained without much expenditure and are quite fast in genomic analysis. The EST sequences can be used to search the homologous organisms in different databases such as NCBI (National Centre for Biotechnology Information). Thus we can collect information on expression patterns of different species. Therefore, they play vital role in discovery of gene and genome analysis. _____________________________________________________________________ Cistron (or gene) is a portion of DNA which specifically transcribe to form mRNA and finally helps in synthesis of protein. -------------------------------------------------------------------------------- *Generation of Expressed Sequence Tags:* The presence of introns makes gene identification quite difficult. The DNA is firstly transcribed to mRNA which is the key for synthesis of building blocks i.e. proteins by a process called translation. Interestingly, mRNAs do not contain the sequence transcribed from introns. Thus mRNA isolation is the key for ESTs construction. mRNA is quite unstable outside the cell, therefore reverse transcription id performed to convert it to cDNA, which is comparatively stable. -------------------------------------------------------------------------------- Translation is the process of protein synthesis from mRNA on the surface of ribosomes. ---------------------------------------------------------------------------------------------