Small nuclear RNA

The abbreviation stands for snRNA small nuclear ribonucleic acid, which small nuclear ribonucleic acid means. RNA is from about 100 to 300 base pairs. SnRNA is localized in the nucleus, and is manufactured by the polymerases of RNA polymerase II and III.

SnRNP complexes

SnRNA molecules associate in the nucleus with several specific proteins to form a complex, the snRNP ( small nuclear ribonucleoprotein particle; snurp spoken). Exceptions to this type 2 introns that do not overlap with proteins. Due to the high uracil content, the various snRNP species also U1 snRNA, U2 snRNA etc. may be mentioned. Five of these snRNPs form the so called spliceosome. From individual snRNPs, there are up to one million copies. However, only four ingredients for the formation of the spliceosome and for the splicing of pre-mRNA are essential. The spliceosome is constructed with five different RNAs from four snRNP (U1, U2, U4/U6 and U5). Seven proteins are present in each snRNP. They are referred to as Sm proteins and LSM proteins ( Sm- like proteins). They form an annular structure which probably surrounds the snRNA. All other proteins present in a snRNP, are specific to the respective snRNP type. All U- snRNAs exhibit pronounced secondary structures. While the nucleotide sequence in various animal and plant species are significantly different, the tertiary structure is highly conserved. At the 5 ' end of the U1, U2, U4 and U5 snRNA is one N, N ,7- Trimethylguanin cap. This forms a 5' -5'- Triphosphatbrücke from one to the next nucleotide. These four U- snRNAs are transcribed by RNA polymerase II. The U6 snRNA does not have N, N ,7- Trimethylguanin cap. Instead, can be found at the 5'- end of a Methyltriphosphat. The transcription of the U6 snRNA is carried out by RNA polymerase III. The three types of snRNP U1, U2 and U5, are made of a RNA molecule, whereas the U4 and U6 snRNA consist of two RNA molecules that bind to each other via hydrogen bonding.

Tasks of the snRNA

As a component of the spliceosome snRNA is catalytically active. It is responsible for the recognition and the splicing of the introns present in the cell nucleus pre-mRNA. SnRNPs bind to conserved sequence segments to the pre-mRNA, which are located at the junction between exon and intron ( 5 'and 3' splice sites ). The in splicing in pre- mRNA introns occurring which are non-coding, is eliminated. Only get the coding exons remain and are linked to the mRNA. Next splicing snRNA is involved in many other processes. These include among others the regulation of RNA polymerase II and several transcription factors. Furthermore snRNA is responsible for the integrity of the telomeres of the chromosomes.

The snoRNA

The snoRNA (small nucleolar Ribonucleic Acid ) is a large subset of the snRNA. snoRNA is on the chemical modification of tRNA ( transfer RNA ), rRNA (ribosomal RNA) and snRNA involved, and moreover, responsible for RNA production. snoRNA is to be found in the nucleolus, but also in the cajal bodies of eukaryotes.