Small nuclear RNA
Encyclopedia
Small nuclear ribonucleic acid (snRNA) is a class of small RNA molecules that are found within the nucleus of eukaryotic cells. They are transcribed by RNA polymerase II
or RNA polymerase III
and are involved in a variety of important processes such as RNA splicing (removal of intron
s from hnRNA), regulation of transcription factors (7SK RNA
) or RNA polymerase II
(B2 RNA), and maintaining the telomere
s. They are always associated with specific proteins, and the complexes are referred to as small nuclear ribonucleoprotein
s (snRNP) often pronounced "snurps". These elements are rich in uridine
content.
A large group of snRNAs are known as small nucleolar RNAs
(snoRNAs). These are small RNA molecules that play an essential role in RNA biogenesis
and guide chemical modifications of ribosomal RNAs (rRNAs) and other RNA genes (tRNA and snRNAs). They are located in the nucleolus
and the Cajal bodies
of eukaryotic cells (the major sites of RNA synthesis).
RNA polymerase II
RNA polymerase II is an enzyme found in eukaryotic cells. It catalyzes the transcription of DNA to synthesize precursors of mRNA and most snRNA and microRNA. A 550 kDa complex of 12 subunits, RNAP II is the most studied type of RNA polymerase...
or RNA polymerase III
RNA polymerase III
RNA polymerase III transcribes DNA to synthesize ribosomal 5S rRNA, tRNA and other small RNAs. The genes transcribed by RNA Pol III fall in the category of "housekeeping" genes whose expression is required in all cell types and most environmental conditions...
and are involved in a variety of important processes such as RNA splicing (removal of intron
Intron
An intron is any nucleotide sequence within a gene that is removed by RNA splicing to generate the final mature RNA product of a gene. The term intron refers to both the DNA sequence within a gene, and the corresponding sequence in RNA transcripts. Sequences that are joined together in the final...
s from hnRNA), regulation of transcription factors (7SK RNA
7SK RNA
-External links:...
) or RNA polymerase II
RNA polymerase II
RNA polymerase II is an enzyme found in eukaryotic cells. It catalyzes the transcription of DNA to synthesize precursors of mRNA and most snRNA and microRNA. A 550 kDa complex of 12 subunits, RNAP II is the most studied type of RNA polymerase...
(B2 RNA), and maintaining the telomere
Telomere
A telomere is a region of repetitive DNA sequences at the end of a chromosome, which protects the end of the chromosome from deterioration or from fusion with neighboring chromosomes. Its name is derived from the Greek nouns telos "end" and merοs "part"...
s. They are always associated with specific proteins, and the complexes are referred to as small nuclear ribonucleoprotein
SnRNP
snRNPs , or small nuclear ribonucleoproteins, are RNA-protein complexes that combine with unmodified pre-mRNA and various other proteins to form a spliceosome, a large RNA-protein molecular complex upon which splicing of pre-mRNA occurs...
s (snRNP) often pronounced "snurps". These elements are rich in uridine
Uridine
Uridine is a molecule that is formed when uracil is attached to a ribose ring via a β-N1-glycosidic bond.If uracil is attached to a deoxyribose ring, it is known as a deoxyuridine....
content.
A large group of snRNAs are known as small nucleolar RNAs
SnoRNA
Small nucleolar RNAs are a class of small RNA molecules that primarily guide chemical modifications of other RNAs, mainly ribosomal RNAs, transfer RNAs and small nuclear RNAs...
(snoRNAs). These are small RNA molecules that play an essential role in RNA biogenesis
Biogenesis
Biogenesis is the law that living things come only from other living things, e.g. a spider lays eggs, which develop into spiders. It may also refer to biochemical processes of production in living organisms.-Spontaneous generation:...
and guide chemical modifications of ribosomal RNAs (rRNAs) and other RNA genes (tRNA and snRNAs). They are located in the nucleolus
Nucleolus
The nucleolus is a non-membrane bound structure composed of proteins and nucleic acids found within the nucleus. Ribosomal RNA is transcribed and assembled within the nucleolus...
and the Cajal bodies
Cajal body
Cajal bodies are spherical sub-organelles of 0.3-1.0 µm in diameter found in the nucleus of proliferative cells like embryonic cells and tumor cells, or metabolically active cells like neurons. In contrast to cytoplasmic organelles, CBs lack any phospholipid membrane which would separate their...
of eukaryotic cells (the major sites of RNA synthesis).