Question

what is the function of m7G cap and poly(A)tail in eukaryotic gene ??

Answer 1

m7G cap and poly(A) tail are found at the mRNA of eukaryotes only because mRNA processing only found in eukaryotes.

function of m7G cap:
-gives mRNA protection in the nucleus by preventing pre-mRNA degradation.
-marks the 5' end of mRNA and this is to help cells to distinguish mRNA from other RNA
- binds with cap-binding complex(CBC) to mark the completion of 5'capping so that mRNA is ready for export to cytosol. The CBC dissociates from MRNA after the mRNA is exported out from nucleus to cytosol so that CBC can re-enter nucleus to help to export another mRNA
-after mRNA export and the dissociation of CBC, the free m7G cap will bind with eukaryotic initiation factors(eIFs) for translation
- the m7G cap serves as ribosome binding site, in other words ribosome recognises the cap and bind to the 5' end of mRNA

function of poly(A) tail:
-slowing down mRNA degradation in cytoplasm (just like m7G cap)
- binds with poly-A binding protein(PABP) to mark the completion of poly-A addition so that mRNA is ready for export to cytosol.
-the poly-A tail also helps translation because the PABP (still bind on the poly-A tail after mRNA export) will bind with eIFs (which will bind with m7G cap) and the mRNA will coil into a loop so that many ribosomes can bind on the coiled mRNA and many initiation of translation can take place, increasing the efficiency of translation.

I hope this will help you. Please correct me if i'm wrong.