06-16-2014, 07:35 PM
SnoRNA – Small Nucleolar RNA
Small nucleolar RNAs also fall into the category of small RNA molecules. Their main function is related to the chemical modification of other RNA molecules and based on that, they are divided into two classes: H/ACA box snoRNAs, responsible for pseudoridylation, and C/D box snoRNAs, responsible for methylation. Pseudoridylation is the production of pseudoridine from uridine through post-transcriptional isomerization. Methylation is the addition of the methyl group to the substrate.
Small nucleolar RNA molecules usually affect ribosomal RNAs, transfer RNAs and small nuclear RNAs. They do so while the targets are still in their pre-mRNA forms and they affect only one or two modifications made on a single molecule of RNA with the help of several other proteins forming snoRNP complex (small nucleolar ribonucleoprotein).
The first step is the recognition of the target sequence through the complementary antisense sequence 10-20 nucleotides long. The second step is the methylation or pseudoridylation. These modifications affect the RNA folding and interaction with ribosomal proteins. Moreover, pseudoridylation adds the possibility for another hydrogen bond, while methylation protects RNA from hydrolysis.
Interestingly, research has shown that some small nucleolar RNAs, whose targets are snRNAs (small nuclear RNAs) function in both methylation and pseudoridylation. These molecules contain both H/ACA and C/D boxes and they are also called Cajal body-specific RNAs because they accumulate in the Cajal body (while most of the other snoRNAs are found in the nucleolus).
Additional functions
Some micro RNA molecules actually start off as small nucleolar RNAs only to be processed into miRNAs. Some of these were first identified as miRNAs with functions (targets) different than those of regular miRNAs, but later on, it was shown that they are actually modified snoRNAs.
Some studies have found that small nucleolar RNAs do not always have to target rRNAs. It has been shown that some snoRNAs can actually control the chromatin structure, its condensation and accessibility. Other studies have shown that some snoRNAs are active during the alternative splicing; namely, they regulate the splicing of trans genes.
Small nucleolar RNAs also fall into the category of small RNA molecules. Their main function is related to the chemical modification of other RNA molecules and based on that, they are divided into two classes: H/ACA box snoRNAs, responsible for pseudoridylation, and C/D box snoRNAs, responsible for methylation. Pseudoridylation is the production of pseudoridine from uridine through post-transcriptional isomerization. Methylation is the addition of the methyl group to the substrate.
Small nucleolar RNA molecules usually affect ribosomal RNAs, transfer RNAs and small nuclear RNAs. They do so while the targets are still in their pre-mRNA forms and they affect only one or two modifications made on a single molecule of RNA with the help of several other proteins forming snoRNP complex (small nucleolar ribonucleoprotein).
The first step is the recognition of the target sequence through the complementary antisense sequence 10-20 nucleotides long. The second step is the methylation or pseudoridylation. These modifications affect the RNA folding and interaction with ribosomal proteins. Moreover, pseudoridylation adds the possibility for another hydrogen bond, while methylation protects RNA from hydrolysis.
Interestingly, research has shown that some small nucleolar RNAs, whose targets are snRNAs (small nuclear RNAs) function in both methylation and pseudoridylation. These molecules contain both H/ACA and C/D boxes and they are also called Cajal body-specific RNAs because they accumulate in the Cajal body (while most of the other snoRNAs are found in the nucleolus).
Additional functions
Some micro RNA molecules actually start off as small nucleolar RNAs only to be processed into miRNAs. Some of these were first identified as miRNAs with functions (targets) different than those of regular miRNAs, but later on, it was shown that they are actually modified snoRNAs.
Some studies have found that small nucleolar RNAs do not always have to target rRNAs. It has been shown that some snoRNAs can actually control the chromatin structure, its condensation and accessibility. Other studies have shown that some snoRNAs are active during the alternative splicing; namely, they regulate the splicing of trans genes.
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