Малые ядрышковые РНК: различия между версиями

 

=== C/D box ===

C/D box snoRNAs contain two short conserved sequence motifs, C (UGAUGA) and D (CUGA) located near the [[5']] and [[3']] ends of the snoRNA respectively. Short regions (~ 5 nucleotides) located [[upstream_(molecular_biology) | upstream]] of the C box and [[downstream_(molecular_biology) |downstream]] of the D box are usually base complementary and form a stem-box structure which brings the C and D box motifs into close proximity. This stem-box structure has been shown to be essential for correct snoRNA synthesis and nucleolar localization <ref>{{cite journal | last = Samarsky | first = DA | coauthors = Fournier MJ, Singer RH, Bertrand E | year = 1998 | title = The snoRNA box C/D motif directs nucleolar targeting and also couples snoRNA synthesis and localization | journal = EMBO | volume = 17 | pages = 3747–3757 | pmid = 9649444 | doi = 10.1093/emboj/17.13.3747 }} </ref>. Many C/D box snoRNA also contain an additional less well conserved copy of the C and D motifs (referred to as C' and D') located in the central portion of the snoRNA molecule. A conserved region of 10-21 nucleotides upstream of the D box is complementary to the methylation site of the target RNA and enables the snoRNA to form and RNA duplex with the RNA <ref>{{cite journal | author = Kiss-László Z, Henry Y, Kiss T | title = Sequence and structural elements of methylation guide snoRNAs essential for site-specific ribose methylation of pre-rRNA | journal = EMBO J. | volume = 17 | issue = 3 | pages = 797–807 | year = 1998 | pmid = 9451004 | doi = 10.1093/emboj/17.3.797 }}</ref>. The nucleotide to be modified in the target RNA is usually located at the 5th position upstream from the D box (or D' box) <ref>{{cite journal | author = Cavaillé J, Nicoloso M, Bachellerie JP | title = Targeted ribose methylation of RNA in vivo directed by tailored antisense RNA guides | journal = Nature | volume = 383 | issue = 6602 | pages = 732–5 | year = 1996 | pmid = 8878486 | doi = 10.1038/383732a0 | issn = }}</ref> <ref >{{cite journal | author = Kiss-László Z, Henry Y, Bachellerie JP, Caizergues-Ferrer M, Kiss T | title = Site-specific ribose methylation of preribosomal RNA: a novel function for small nucleolar RNAs | journal = Cell | volume = 85 | issue = 7 | pages = 1077–88 | year = 1996 | pmid = 8674114 | doi = | issn = }}</ref>. Box C/D snoRNAs associate with four evolutionary conserved and essential proteins ([[Fibrillarin]] (Nop1p), Nop56p, Nop58p and Snu13) which make up the core C/D box snoRNP <ref name=Bachellerie />.