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Small nuclear RNA (snRNA) is a class of small RNA molecules that are found within the splicing speckles and Cajal bodies of the cell nucleus in eukaryotic cells. The length of an average snRNA is approximately 150 nucleotides. They are transcribed by either RNA polymerase II or RNA polymerase III. [1]
This variant class of snRNPs includes: U11 snRNA, U12 snRNA, U4atac snRNA, and U6atac snRNA. While different, they perform the same functions as do U1, U2, U4, and U6, respectively. [5] Additionally, U7 snRNP is made of U7 small nuclear RNA and associated proteins and is involved in the processing of the 3′ stem-loop of histone pre-mRNA. [1]
An unusual guide snoRNA U85 that functions in both 2′-O-ribose methylation and pseudouridylation of small nuclear RNA (snRNA) U5 has been identified. [14] This composite snoRNA contains both C/D and H/ACA box domains and associates with the proteins specific to each class of snoRNA (fibrillarin and Gar1p, respectively).
Small nuclear RNA (snRNA) molecules bind to specific proteins to form a small nuclear ribonucleoprotein complex (snRNP, pronounced "snurps"), which in turn combines with other snRNPs to form a large ribonucleoprotein complex called a spliceosome. The spliceosome removes introns from a transcribed pre-mRNA, a type of primary transcript.
Introns are spliced out of pre-mRNA by spliceosomes, which contain several small nuclear RNAs (snRNA), [7] or the introns can be ribozymes that are spliced by themselves. [60] RNA can also be altered by having its nucleotides modified to nucleotides other than A, C, G and U.
U2 spliceosomal snRNAs are a species of small nuclear RNA molecules found in the major spliceosomal (Sm) machinery of virtually all eukaryotic organisms. In vivo, U2 snRNA along with its associated polypeptides assemble to produce the U2 small nuclear ribonucleoprotein (), an essential component of the major spliceosomal complex. [1]
U1 spliceosomal RNA is the small nuclear RNA (snRNA) component of U1 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.
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 that catalyzes the excision of introns from pre-mRNA.