In prokaryotes, two classes of transcription terminators are known:
- Intrinsic transcription terminators where a hairpin structure forms within the nascent transcript that disrupts the mRNA-DNA-RNA polymerase ternary complex.
- Rho-dependent transcription terminators that require Rho factor, an RNA helicase protein complex to disrupt the nascent mRNA-DNA-RNA polymerase ternary complex.
In eukaryotes, terminators are recognized by protein factors that co-transcriptionally cleave the nascent RNA at a polyadenylation signal, halting further elongation of the transcript by RNA polymerase. The subsequent addition of the poly-A tail at this site stabilizes the mRNA and allows it to be exported outside the nucleus.
A transcription terminator must also be distinguished from the dideoxynucleotides added to a dye terminator sequencing.
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