They occur if polyadenylation signal sequence (5'- AAUAAA-3') is present in pre-mRNA, which is usually between protein-coding sequence and terminator.
Proses ini terjadi jika sekuens sinyal poliadenilasi (5'- AAUAAA-3 ') hadir dalam pre-mRNA, yang biasanya antara sekuens kode protein dan terminator.