Small nucleolar RNA

FIGURE 26-22 Processing of pre-rRNA transcripts in vertebrates. In step (T), the 45S precursor is methylated at more than 100 of its 14,000 nucleotides, mostly on the 2 -OH groups of ribose units retained in the final products. (5) A series of enzymatic cleavages produces the 18S, 5.8S, and 28S rRNAs. The cleavage reactions require RNAs found in the nucleolus, called small nucleolar RNAs (snoRNAs), within protein complexes reminiscent of spliceosomes. The 5S rRNA is produced separately. 

Polymerase II Transcription of most genes to give precursors to mRNA and most small nuclear RNAs (snRNAs and small nucleolar RNAs (snoRNAs)... 

Figure 4.4 Nucleolar localized anti-HIV-1 ribozyme. The anti-HIV-1 ribozyme was inserted within the apical loop of the small nucleolar RNA U16. The chimeric U16-ribozyme was placed behind the Pol III U6 snRNA promoter. Transcripts of the chimeric RNA localize to the nucleolus, as shown by the in situ hybridization and co-localization with the small nucleolar RNA U3. The in situ hybrids were performed in transfected 293 cells. The ribozyme probe was fluorescein labeled (green), whereas the U3 probe was labeled with Cy3 (red). Reproduced with permission from Michienzi et al. (2000). (see Color Plate 3)...

Solnble iV-ethylmaleimide-sensitive fnsion (NSF A -ethylmaleimide-sensitive factor) protein attachment protein receptors can be either R-SNAREs or Q-SNARES depending on sequence homologies SNARE motif Small nucleolar RNA Single nucleotide polymorphism Small nuclear RNA... 

RNA population of a cell. The cell contains highly abundant ribosomal RNA, transfer RNA, microRNA, small nucleolar RNA, small nuclear RNA, and additional rare types of RNA, but the focus of this review is on the protein-coding mRNA transcripts. The maturation of these protein-coding transcripts consists of several distinct steps, aU of which are regulated specifically (Fig. 1)... 

Cavaille J, Buiting K, Kiefmann M, Lalande M, Brannan Cl, Horsthemke B, et al. Identification of brain-specific and imprinted small nucleolar RNA genes exhibiting an unusual genomic organization. Proc Natl Acad Sci USA 2000 97 14311-6. 

Runte M, Huttenhofer A, Gross S, Kiefmann M, Horsthemke B, Buiting K. The IC-SNURE-SNRPN transcript serves as a host for multiple small nucleolar RNA species and as an antisense RNA for UBE3A. Hum Molec Genet 2001 10 2687-2700. 

Small interfering RNA, see siRNA Small molecule therapeutic target (SMT) 104 Small nucleolar RNA, see snoRNA Small nucleolar RNP, see snoRNP Small organic molecules, in disease targeting 1275... 

Small Nucleolar RNAs Assist in Processing Pre-rRNAs and Assembling Ribosome Subunits... 

A FIGURE 12-34 Processing of pre-rRNA and assembly of ribosomes in higher eukaryotes. Ribosomal and nucleolar proteins associate with 45S pre-RNA as it is synthesized, forming an SOS pre-rRNR Sites of cleavage and chemical modifications are determined by small nucleolar RNAs (not shown). Note that synthesis of 5S rRNA occurs outside the nucleolus. 

Kiss-Laszlo, Z., Henry, Y., Bachellerie, et al. (1996) Site-specific ribose methylation of preribosomal RNA A novel function for small nucleolar RNAs. Cell 85 1077. 

Small nucleolar RNAs (snoRNAs) contain between 60 and 300 nucleotides. They bind to specific target sequences by hydrogen-bond base pairing and then specialized proteins bind to the complex. The complex catalyzes modifications of the target RNA molecule, thus snoRNAs are particularly important in processing rRNA in mammals. 

Noncoding RNA is RNA that is generated by transcription from DNA but that is not translated into protein. It inclndes the major strnctnral RNAs rRNA and tRNA as well as small nuclear RNA (snRNA), small nucleolar RNA (snoRNA), microRNA (miRNA), and short interfering RNA (siRNA). 

This is small nucleolar RNA or snoRNA. These RNA species recognize their target sequence by base-pairing and then recruit specialized proteins that perform nucleotide modifications to these RNAs usually 2 O-ribose methylation, base deaminations such as adenine-to-inosine conversions, and the addition of pseudouridines. These modifications are crucial to ribosome biogenesis. 

Transport of RNA between the nucleus and cytoplasm is an essential step in the expression of messenger RNA (mRNA), and the function of ribosomal RNA (rRNA), transfer RNA (tRNA), and small nuclear RNA (snRNA). Most nuclear RNA transcripts are covalently modified, complexed with proteins into ribo-nucleoprotein particles (RNPs), and then exported through the nuclear pore complex to the cytoplasm. After export, most RNAs remain in the cytoplasm where they function in protein synthesis. However, many snRNAs are imported back to the nucleus as mature snRNP particles, where they function in pre-mRNA splicing. Small nucleolar RNAs (snoRNAs), which function in ribosome biogenesis, are not exported to the cytoplasm, but their intranuclear targeting to the nucleolus is an area of active research. 

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