Expressed Sequence Tag
Expressed Sequence Tags ( EST ) are short DNA sequences of mostly 100-800 base pairs in length by the partial sequencing of cDNAs derived from the 5 'or 3' end. Since cDNAs are generated by the reverse transcription of mRNA , ESTs represent a section of the sequence of genes that are expressed in the living being, tissue or cell type under consideration, i.e. are active. In comparison to complete cDNA sequences or genome sequencing, ESTs can be generated with relatively little effort. The sequence information obtained can then be fed into an EST database and used as a basis for further analyzes by means of sequence comparisons and bioinformatic methods. ESTs always go back to a single sequencing, whereby different cDNAs can be copied and sequenced to different degrees. This and the partially random approach of EST extraction methods mean that ESTs sequences are relatively unreliable. Since ESTs only represent the sequences of mature mRNAs, introns , promoters and other regulatory elements of genes are not present in EST databases .
Applications for ESTs
- Genome landmarks: Since ESTs mostly represent sequences that only occur once in a genome, they can serve as points of reference when assembling the sequence data that arise as part of genome sequencing. This played e.g. B. plays a crucial role in decoding the human genome.
- Expression analysis: The occurrence and frequency of ESTs can provide rough information on the expression of the genes in question. This method is sometimes referred to as Virtual Northern Blot based on the Northern Blot .
- Identification of unknown genes: By comparing ESTs with the sequences of known genes, related genes can be identified in the same or in different organisms. The ESTs can then serve as a gene probe to determine the entire sequence of the gene in question, e.g. B. in a cDNA library or by means of RACE-PCR .
literature
- Shivashankar H. Nagaraj, Robin B. Gasser, Shoba Ranganathan: A hitchhiker's guide to expressed sequence tag (EST) analysis . In: Briefings in Bioinformatics . tape 8 , no. 1 , 2006, p. 6–21 (English, full text [PDF; 199 kB ]).
- EST factsheets at NCBI
Individual evidence
- ↑ Adams MD, Kelley JM, Gocayne JD, et al .: Complementary DNA sequencing: expressed sequence tags and human genome project. In: Science . tape 252 , 1991, pp. 1651-1656 (English).
- ↑ User manual for the Virtual Northern blot ( Memento of the original from March 4, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
