Small Cajal body specific RNA 15 (also known as SCARNA15 or ACA45) is a small nucleolar RNA found in 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...

 and believed to be involved in the pseudouridylation (isomerisation

Isomerisation

In chemistry isomerisation is the process by which one molecule is transformed into another molecule which has exactly the same atoms, but the atoms are rearranged e.g. A-B-C → B-A-C . In some molecules and under some conditions, isomerisation occurs spontaneously...

 of 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....

 to pseudouridine

Pseudouridine

Pseudouridine is the C-glycoside isomer of the nucleoside uridine, and it is the most prevalent of the over one hundred different modified nucleosides found in RNA. Ψ is found in all species and in many classes of RNA except mRNA...

) of U1 spliceosomal RNA

U1 spliceosomal RNA

U1 spliceosomal RNA is the small nuclear RNA component of U1 snRNP , 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...

.

scaRNAs are a specific class of small nucleolar RNAs that localise to 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...

 and guide the modification of 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...

 transcribed spliceosomal

Spliceosome

A spliceosome is a complex of snRNA and protein subunits that removes introns from a transcribed pre-mRNA segment. This process is generally referred to as splicing.-Composition:...

 RNAs U1

U1 spliceosomal RNA

U1 spliceosomal RNA is the small nuclear RNA component of U1 snRNP , 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...

, U2

U2 spliceosomal RNA

U2 spliceosomal RNA is a small nuclear RNA component of the spliceosome . Complementary binding between U2 snRNA and the branchpoint sequence of the intron results in the bulging out of an unpaired adenosine, on the BPS, which initiates a nucleophilic attack at the intronic 5' splice...

, U4

U4 spliceosomal RNA

The U4 small nuclear Ribo-Nucleic Acid is a non-coding RNA component of the major or U2-dependent spliceosome – a eukaryotic molecular machine involved in the splicing of pre-messenger RNA...

, U5

U5 spliceosomal RNA

U5 RNA is a non-coding RNA that is a component of both types of known spliceosome. The precise function of this molecule is unknown, though it is known that the 5' loop is required for splice site selection and p220 binding, and that both the 3' stem-loop and the Sm site are important for Sm...

 and U12

U12 minor spliceosomal RNA

U12 minor spliceosomal RNA is formed from U12 small nuclear , together with U4atac/U6atac, U5, and U11 snRNAs and associated proteins, forms a spliceosome that cleaves a divergent class of low-abundance pre-mRNA introns. Although the U12 sequence is very divergent from that of U2, the two are...

.

ACA45 belongs to the H/ACA box class of guide RNAs as it has the predicted hairpin-hinge-hairpin-tail structure, the conserved H/ACA-box motifs and is found associated with GAR1 . ACA45 is predicted to guide the pseudouridylation of residue U37 of the U2 spliceosomal snRNA .

It has been shown that human ACA45 can be processed into a 21 nucleotides long mature miRNA

Mirna

Mirna may refer to:geographical entities* Mirna , a river in Istria, Croatia* Mirna , a river in Slovenia, tributary of the river Sava* Mirna , a settlement in the municipality of Mirna in Southeastern Sloveniapeople...

 by the RNAse III family endoribonuclease

RNase III

RNase III enzymes specifically bind to and cleave double-stranded RNA . There are three subdivisions, known as Class 1, 2, and 3.Prokaryotic ribonuclease III is an enzyme that digests double-stranded RNA. It is involved in the processing of ribosomal RNA precursors and of some mRNAs.* Class 1...

 dicer

Dicer

Dicer is an endoribonuclease in the RNase III family that cleaves double-stranded RNA and pre-microRNA into short double-stranded RNA fragments called small interfering RNA about 20-25 nucleotides long, usually with a two-base overhang on the 3' end...

. This snoRNA product has previously been identified as mmu-miR-1839 and was shown to be processed independent of the other miRNA generating endoribonuclease

Endoribonuclease

A Endoribonuclease is a ribonuclease endonuclease. It cleaves either single-stranded or double-stranded RNA, depending on the enzyme. Example includes both single proteins like RNase III, RNase A, RNase T1, and RNase H, and also complexes of proteins like RNase P and the RNA-induced silencing...

 drosha

Drosha

Drosha is a Class 2 RNase III enzyme responsible for initiating the processing of microRNA , or short RNA molecules naturally expressed by the cell that regulate a wide variety of other genes by interacting with the RNA-induced silencing complex to induce cleavage of complementary messenger RNA ...

.