In: Biology
The poly-A tails in eukaryotic cell functions as stabilizers of
mRNAs. They are a long chain of adenine which is to be added to a
messenger RNA molecule while processing the RNA before it is
prepared for protein synthesis. The process of polyadenylation of
RNA occurs inside the nucleus. As soon as the eukaryotic cell's DNA
is transcribed into RNA, initially called the primary RNA
transcript, it undergoes various modifications like capping,
tailing, intron splicing and histone mRNA processing until it's
maturity. These modifications prevent the RNA from degradation
outside the nucleus and allow the RNA to take part in protein
synthesis.
During the adenylation process, the 3' end of the primary RNA
transcript is cleaved which is necessary to obtain a free 3'
hydroxyl. Next, the poly-A polymerase enzyme starts adding a chain
of adenine nucleotides to the end. During this process, 100-250
long residues of poly-A tails are added in the eukaryotic cells and
around 70-80 long residues in prokaryotes. The modifications
somehow are stable in relatively long poly-A tails. The survival
chance ranges from 30 minutes to hours or throughout the lifetime
of that mRNA until it is translated to proteins. Sometimes very
short oligo -A tails can result in decay of the RNA which was first
reported in bacteria. These short oligo-A tails sometimes promote
the entry of 3' exonucleolytic degradation.
The poly-A tails help in controlling the RNA turnover, long tails
prevent decay whereas the short tails promote it. Degradation
doesn't take place beyond a certain threshold. Further, this
modification provides stimulation of translation initiation process
which involves interaction between the poly-A binding protein in
the cytoplasm and the translation initiation factor eIF4G.