In eukaryotic organisms, the mechanism of transcription termination of protein-coding genes involves two different processes: 1-the site-specific cleavage of the precursor messenger RNA (pre-mRNA) sequence in the 3'-untranslated region (3'-UTR), and 2- the separation of RNA polymerase II (Pol II) from the DNA template. In regard to the cleavage of the pre-mRNA, it is a process followed by the polyadenylation (polyA) of the upstream cleaved product. The main function of the polyA tail is to protect the mRNA from enzymatic degradation. Moreover, the mechanism of transcription termination is accompanied by dephosphorylation of the C-terminal domain (CTD) of the large subunit of the RNA Pol II.
