Читать книгу Algorithms in Bioinformatics - Paul A. Gagniuc - Страница 19

The DNA region of the gene can be subdivided into other types of regions. Especially in eukaryotes, many genes are organized into coding (exons) and noncoding regions (spliceosomal introns). Both exons and introns are transcribed into a continuous pre-mRNA fragment. While the pre-mRNA is being transcribed/synthesized, the intronic regions are removed by spliceosomes (a ribonucleoprotein complex) and the ligation of the exon regions forms the mRNA. The process of intron removal is called splicing. Exon ligation in the same order, in which these regions appear in a gene, is called constitutive splicing. Thus, constitutive splicing allows for a “one gene–one protein” model (or, one pre-mRNA – one mRNA). When exon ligation does not follow the order observed in the gene (i.e. certain exons are skipped), several mRNA variants are produced from a single pre-mRNA variant. If the gene encodes for proteins, then each mRNA variant will generate a different type of protein (protein isoforms). This process is known as alternative splicing, and is responsible for the exaggerated abundance of protein types in the eukaryotic proteome.