Terminator (genetics)

In genetics, a terminator, or transcription terminator is a section of genetic sequence that marks the end of gene or operon on genomic DNA for transcription.

In prokaryotes, two classes of transcription terminators are known:
 * 1) Intrinsic transcription terminators where a hairpin structure forms within the nascent transcript that disrupts the mRNA-DNA-RNA polymerase ternary complex.
 * 2) 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.

Terminator sequences are distinct from termination codons that occur in the mRNA and are the stopping signal for translation, which may also be called nonsense codons.

A transcription terminator must also be distinguished from the dideoxynucleotides added to a dye terminator sequencing.