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Signal recognition particle RNA
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<p>The signal recognition particle RNA, (also known as 7SL, 6S, <a href="http://www.wikigenes.org/e/gene/e/947102.html">ffs</a>, or 4.5S RNA) is part of the <a href="/facts/Signal_recognition_particle/J9K0m2Mw">signal recognition particle</a> (SRP) <a href="/facts/Ribonucleoprotein/S07sU6hq">ribonucleoprotein</a> complex. SRP recognizes the <a href="/facts/Signal_peptide/9oARjq52">signal peptide</a> and binds to the <a href="/facts/Ribosome/CF2u2gtg">ribosome</a>, halting protein synthesis. <a href="/facts/Signal_recognition_particle_receptor/gyKNV6wE">SRP-receptor</a> is a protein that is embedded in a membrane, and which contains a <a href="/facts/Transmembrane_channels/hL8W84kp">transmembrane pore</a>. When the SRP-ribosome complex binds to SRP-receptor, SRP releases the ribosome and drifts away. The ribosome resumes protein synthesis, but now the protein is moving through the SRP-receptor transmembrane pore. </p><p>In this way SRP directs the movement of <a href="/facts/Proteins/Jxmagu3E">proteins</a> within the <a href="/facts/Cell_(biology)/bLM9UQvy">cell</a> to bind with a transmembrane pore which allows the protein to cross the membrane to where it is needed. The RNA and protein components of this complex are highly <a href="/facts/Conserved_sequence/YAxy2Xa2">conserved</a> but do vary between the different <a href="/facts/Kingdom_(biology)/QGRKbHos">kingdoms</a> of life. </p><p>The common <a href="/facts/Short_interspersed_nuclear_element/6eG8Umm5">SINE</a> family <a href="/facts/Alu_sequence/BjQeUY7Y">Alu</a> probably originated from a 7SL RNA gene after deletion of a central sequence. </p><p>The <a href="/facts/Eukaryotic/SkwyPLMA">eukaryotic</a> SRP consists of a 300-nucleotide 7S <a href="/facts/RNA/HxPeNfNj">RNA</a> and six proteins: SRPs 72, 68, 54, 19, 14, and 9. Archaeal SRP consists of a 7S RNA and homologues of the eukaryotic SRP19 and SRP54 proteins. Eukaryotic and archaeal 7S RNAs have very similar secondary structures. </p><p>In most <a href="/facts/Bacteria/wC8xSCsU">bacteria</a>, the SRP consists of an RNA molecule (4.5S) and the Ffh protein (a homologue of the eukaryotic SRP54 protein). Some <a href="/facts/Gram-positive/H6WYQ17e">Gram-positive</a> bacteria (e.g. <i><a href="/facts/Bacillus_subtilis/KA8AodsE">Bacillus subtilis</a></i>) have a longer eukaryote-like SRP RNA that includes an <a href="/facts/Alu_domain/BjQeUY7Y">Alu domain</a>. </p><p>In eukaryotes and archaea, eight helical elements fold into the <a href="/facts/Alu_sequence/BjQeUY7Y">Alu</a> and S domains, separated by a long linker region. The Alu domain is thought to mediate the peptide chain elongation retardation function of the SRP. The universally conserved helix which interacts with the SRP54 M domain mediates signal sequence recognition. The SRP19-helix 6 complex is thought to be involved in SRP assembly and stabilises helix 8 for SRP54. binding Humans have three functional SRP RNA genes, conveniently named RN7SL1, RN7SL2, and RN7SL3. The human genome in particular is known to contain a large amount of SRP RNA related sequence, including <a href="/facts/Alu_sequence/BjQeUY7Y">Alu repeats</a>. </p>