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U6 snRNA is the non-coding small nuclear RNA (snRNA) component of U6 snRNP (''small nuclear ribonucleoprotein''), an RNA-protein complex that combines with other snRNPs, unmodified pre-mRNA, and various other proteins to assemble a spliceosome, a large RNA-protein molecular complex upon which splicing of pre-mRNA occurs. Splicing, or the removal of introns, is a major aspect of post-transcriptional modification, and takes place only in the nucleus of eukaryotes. The RNA sequence of U6 is the most highly conserved across species of all five of the snRNAs involved in the spliceosome, suggesting that the function of the U6 snRNA has remained both crucial and unchanged through evolution. It is common in vertebrate genomes to find many copies of the U6 snRNA gene or U6-derived pseudogenes. This prevalence of "back-ups" of the U6 snRNA gene in vertebrates further implies its evolutionary importance to organism viability. The U6 snRNA gene has been isolated in many organisms, including ''C. elegans''. Among them, Baker's yeast (''Saccharomyces cerevisiae'') is a commonly used model organism in the study of snRNAs. == Role of U6 snRNA == Base-pair specificity of the U6 snRNA allows the U6 snRNP to bind tightly to the U4 snRNA and loosely to the U5 snRNA of a triple-snRNP during the initial phase of the splicing reaction. As the reaction progresses, the U6 snRNA is unzipped from U4 and binds to the U2 snRNA. At each stage of this reaction, the U6 snRNA secondary structure undergoes extensive conformational changes. The association of U6 snRNA with the 5' end of the intron via base-pairing during the splicing reaction occurs prior to the formation of the lariat (or ''lasso-shaped'') intermediate, and is required for the splicing process to proceed. The association of U6 snRNP with U2 snRNP via base-pairing forms the U6-U2 complex, a structure that comprises the active site of the spliceosome. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「U6 spliceosomal RNA」の詳細全文を読む スポンサード リンク
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