For example , a poly ( A ) tail and a 5 ' cap are added to eukaryotic pre-mRNA and introns are removed by the spliceosome .
Primary transcript RNAs are often modified by enzymes after transcription .
A poly ( A ) tail and a 5 ' cap are added to eukaryotic pre-mRNA and introns are removed by the spliceosome .
Primary transcript RNAs are often modified by enzymes after transcription .