After the mRNA is completed and cleaved off at the poly-A signal sequence, the left-over (residual) RNA strand remains bound to the DNA template and the RNA polymerase II unit, continuing to be transcribed. After this cleavage, a so-called exonuclease binds to the residual RNA strand and removes the freshly transcribed nucleotides one at a time (also called 'degrading' the RNA), moving towards the bound RNA polymerase II. This exonuclease is XRN2 (5'-3' Exoribonuclease 2) in humans. This model proposes that XRN2 proceeds to degrade the uncapped residual RNA from 5' to 3' until it reaches the RNA pol II unit. This causes the exonuclease to 'push off' the RNA pol II unit as it moves past it, terminating the transcription while also cleaning up the residual RNA strand.