Polyadenylation

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Polyadenylation.png

As polyadenylation refers to the attachment of adenine - nucleotides , called poly (A) tail at the 3 'end of eukaryotic (including viral ) pre-mRNA by the enzyme poly (A) polymerase . Just like splicing , polyadenylation is a post-transcriptional modification of the eukaryotic pre-mRNA.

The poly (A) tail is not encoded by the DNA , but rather attached to the 3 'end of the pre-mRNA by the enzyme poly (A) polymerase during the processing of the pre-mRNA (hnRNA) in the cell nucleus . The processed mRNA is called poly (A) + mRNA. The length of the poly (A) tail varies from organism to organism (baker's yeast about 80 nucleotides, in mammals about 250 nucleotides).

Many proteins are involved in polyadenylation, e.g. B. the multimeric protein CPSF ( cleavage and polyadenylation specificity factor ), which recognizes the polyadenylation signal ( 5 '… AAUAAA… 3' ). The poly (A) binding protein (PABPN1) binds to the growing poly (A) tail during synthesis. The poly (A) tail shortens with increasing age of the mRNA molecule and regulates its half-life .

The functions of the poly (A) tail have not yet been fully researched, but an increase in the stability of the mRNA through protection against degradation and an increase in translatability are certain. The poly (A) tail is occupied by the poly (A) binding protein (PABP) and is necessary for the initiation of translation . A 7-methylguanosine - nucleotide ( CAP structure ) binds at the 5 'end and also serves to protect the degradation.

A protein complex called an exosome is involved in the breakdown of eukaryotic mRNA .

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