<p><strong>Alternative splicing</strong> is the process that occurs in <a title="Eukaryote" href="http://en.wikipedia.org/wiki/Eukaryote">eukaryotes</a> in which the <a title="Splicing (genetics)" href="http://en.wikipedia.org/wiki/Splicing_%28genetics%29">splicing</a> process of a <a title="Pre-mRNA" href="http://en.wikipedia.org/wiki/Pre-mRNA">pre-mRNA</a> transcribed from one gene can lead to different mature <a title="MRNA" href="http://en.wikipedia.org/wiki/MRNA">mRNA</a> molecules and therefore to different proteins. Also <a title="Virus" href="http://en.wikipedia.org/wiki/Virus">viruses</a> have adapted to this biochemical process when using the protein biosynthesis apparatus.</p><p>When the pre-mRNA has been transcribed from the <a title="DNA" href="http://en.wikipedia.org/wiki/DNA">DNA</a>, it includes several <a title="Intron" href="http://en.wikipedia.org/wiki/Intron">introns</a> and <a title="Exon" href="http://en.wikipedia.org/wiki/Exon">exons</a>. In <a title="Nematode" href="http://en.wikipedia.org/wiki/Nematode">nematodes</a>, the mean is 4-5 exons and introns; in the fruit fly <em><a title="Drosophila melanogaster" href="http://en.wikipedia.org/wiki/Drosophila_melanogaster">Drosophila</a></em> there can be more than 100 introns and exons in one transcribed pre-mRNA. But introns and exons are not yet determined at this stage. This decision is made during the splicing process. The regulation and selection of splice sites is done by Serine/Arginine-residue proteins, or <a title="SR protein" href="http://en.wikipedia.org/wiki/SR_protein">SR proteins</a>. The use of alternative splicing factors leads to a modification of the definition of a &quot;gene&quot;. Some have proposed that a gene should be considered as a twofold information structure:</p>

<li><strong>Alternative selection of cleavage/polyadenylation sites</strong>: this is the only method of splicing which can produce an alternative C-terminus domain in proteins. In this case, different sets of <a title="Polyadenylation" href="http://en.wikipedia.org/wiki/Polyadenylation">polyadenylation</a> sites can be spliced with the other exons. </li> <li><strong>Intron retaining mode</strong>: in this case, instead of splicing out an intron, the intron is retained in the mRNA transcript. However, the intron must be properly encoding for <a title="Amino acid" href="http://en.wikipedia.org/wiki/Amino_acid">amino acids</a>. The intron's code must be properly expressible, otherwise a stop codon or a shift in the <a title="Reading frame" href="http://en.wikipedia.org/wiki/Reading_frame">reading frame</a> will cause the protein to be non-functional. </li>

<div class="editsection" style="FLOAT: right; MARGIN-LEFT: 5px">[<a title="Edit section: Importance in molecular genetics" href="http://en.wikipedia.org/w/index.php?title=Alternative_splicing&amp;action=edit&amp;section=1">edit</a>]</div>

<p>Alternative splicing is of great importance to genetics - it invalidates the old theory of one DNA sequence coding for one <a title="Polypeptide" href="http://en.wikipedia.org/wiki/Polypeptide">polypeptide</a> (the &quot;one-gene-one-protein&quot; hypothesis). External information is needed in order to decide which polypeptide is produced, given a DNA sequence and pre-mRNA. (This does not necessarily negate the <a title="Central dogma of molecular biology" href="http://en.wikipedia.org/wiki/Central_dogma_of_molecular_biology">central dogma of molecular biology</a> which is about the flow of information from genes to proteins). Since the methods of regulation are inherited, the interpretation of a <a title="Mutation" href="http://en.wikipedia.org/wiki/Mutation">mutation</a> may be changed.</p><p>It has been proposed that for <a title="Eukaryote" href="http://en.wikipedia.org/wiki/Eukaryote">eukaryotes</a> it was a very important step towards higher efficiency, because information can be stored much more economically. Several proteins can be encoded in a DNA sequence whose length would only be enough for two proteins in the <a title="Prokaryote" href="http://en.wikipedia.org/wiki/Prokaryote">prokaryote</a> way of coding. Others have noted that it is unnecessary to change the DNA of a gene for the <a title="Evolution" href="http://en.wikipedia.org/wiki/Evolution">evolution</a> of a new protein. Instead, a new way of regulation could lead to the same effect, but leaving the code for the established proteins unharmed.</p>

<p>A common myth is that alternative splicing is responsible for humans supposedly being the most complex animals, saying that humans perform more alternative splicing than the other animals. However, this is not the case. A study conducted on the subject found that &quot;the amount of alternative splicing is comparable, with no large differences between humans and other animals.&quot;<sup class="reference" id="_ref-0"><a title="" href="http://en.wikipedia.org/wiki/Alternative_splicing#_note-0">[1]</a></sup> The &quot;record-holder&quot; for alternative splicing is actually a <em><a title="Drosophila" href="http://en.wikipedia.org/wiki/Drosophila">Drosophila</a></em> gene with 38 000 splice variants called <a title="[[Dscam" href="http://en.wikipedia.org/wiki/Dscam">Dscam</a>]].</p><div class="editsection" style="FLOAT: right; MARGIN-LEFT: 5px">[<a title="Edit section: References" href="http://en.wikipedia.org/w/index.php?title=Alternative_splicing&amp;action=edit&amp;section=2">edit</a>]</div>

<li id="_note-0"><strong><a title="" href="http://en.wikipedia.org/wiki/Alternative_splicing#_ref-0">^</a></strong> <a class="external free" title="http://www.nature.com/ng/journal/v30/n1/abs/ng803.html;jsessionid=BF0AED8347574D063F5E347EC693AE83" href="http://www.nature.com/ng/journal/v30/n1/abs/ng803.html;jsessionid=BF0AED8347574D063F5E347EC693AE83">http://www.nature.com/ng/journal/v30/n1/abs/ng803.html;jsessionid=BF0AED8347574D063F5E347EC693AE83</a> </li>

<div class="editsection" style="FLOAT: right; MARGIN-LEFT: 5px">[<a title="Edit section: External links" href="http://en.wikipedia.org/w/index.php?title=Alternative_splicing&amp;action=edit&amp;section=3">edit</a>]</div>

<li><a class="external text" title="http://www.hhmi.org/bulletin/sept2005/features/splicing.html" href="http://www.hhmi.org/bulletin/sept2005/features/splicing.html">HHMI article on alternative splicing</a> </li> <li><a class="external text" title="http://www.nature.com/ng/journal/v30/n1/abs/ng803.html;jsessionid=BF0AED8347574D063F5E347EC693AE83" href="http://www.nature.com/ng/journal/v30/n1/abs/ng803.html;jsessionid=BF0AED8347574D063F5E347EC693AE83">Study on alternative splicing and complexity</a> </li> <li><a class="external text" title="http://www.stamms-lab.net" href="http://www.stamms-lab.net/">Stamms-lab.net: Research Group dealing with alternative Splicing issues and mis-splicing in human diseases</a> </li> <li><a class="external text" title="http://www.dip.molmed.eu" href="http://www.dip.molmed.eu/">Alternative Splicing of ion channels in the brain, connected to mental and neurological diseases</a> </li>

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