Alternative splicing is a post-transcriptional process that eukaryotic organisms undergo to greatly increase the diversity of their proteome. It allows for the joining of particular exons within a gene in different combinations to generate a variety of unique protein isoforms. For instance, consider a gene that has five sequential exons that are each separated by introns. Through the process of alternative splicing an organism (or particular cell type) could generate distinct proteins by incorporating different exons into the processed RNA strand. One protein isoform might contain exons 1, 2, 3 and 5, while another contains 2, 3, 4 and 5. These isoforms can be functionally distinct, localized to particular cell types, present in only the juvenile form of an organism, or even contribute to certain genetic diseases.
Alternative splicing is accomplished by a multitude of different agents called small nuclear ribonucleoproteins (snRNPS, "Snurps") which are made up of both protein and smaller RNA molecular components. These snRNPs assemble into the functional entity termed a spliceosome. The activity and regulation of splicing variants for a certain gene is influenced by the presence of trans-acting factors (DNA binding proteins) which interact with cis-acting factors (specific sequences within the DNA region) to direct spliceosome assembly and activity to certain sites. The presence and amount of these factors will vary between cell types, which further diversifies the array of splice variants between cell and tissue types within higher organisms.