Eukaryotic pre-mRNAs are processed at their 5' and 3' ends. A cap, consisting of a modified nucleotide and several methyl groups, is added to the 5' end. The cap facilitates the binding of a ribosome, increases the stability of the mRNA, and may affect the removal of introns. Processing at the 3' end includes cleavage downstream of an AAUAAA consensus sequence and the addition of a poly(A) tail.
-Why are pre-mRNAs capped, but tRNAs and rRNAs aren't?

Question

Quizplus · Accepted Answer

The Answer is A protein that adds the 5' cap is associated with RNA polymerase II, which transcribes pre-mRNAs but is absent from RNA polymerase I and III, which transcribe rRNA and tRNAs.

Eukaryotic Pre-MRNAs Are Processed at Their 5' and 3' Ends