Termination signal
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In molecular biology, a termination signal is a sequence that signals the end of transcription or translation.[1] Termination signals are found at the end of the part of the chromosome being transcribed during transcription of mRNA. Termination signals bring a stop to transcription, ensuring that only gene-encoding parts of the chromosome are transcribed.[1] Transcription begins at the promoter when RNA polymerase, an enzyme that facilitates transcription of DNA into mRNA, binds to a promoter, unwinds the helical structure of the DNA, and uses the single-stranded DNA as a template to synthesize RNA.[1] Once RNA polymerase reaches the termination signal, transcription is terminated.[1] In bacteria, there are two main types of termination signals: intrinsic and factor-dependent terminators.[1] In the context of translation, a termination signal is the stop codon on the mRNA that elicits the release of the growing peptide from the ribosome.[2]
Termination signals play an important role in regulating gene expression since they mark the end of a gene transcript and determine which DNA sequences are expressed in the cell.[1] Expression levels of certain genes can be increased by inhibiting signal terminators, known as antitermination, which allows for transcription to continue beyond the termination signal site.[1] This can be desirable under specific cell conditions.[1]
Additionally, sometimes, termination signals are overlooked in transcription and translation, resulting in unwanted transcription or translation past the termination signal.[3] To address this issue, termination signals can be optimized to increase termination efficiency.[3]
The two types of termination signals in bacteria are intrinsic and factor-dependent terminators.[4] Intrinsic termination occurs when a specific sequence on the growing RNA strand elicits detachment of RNA polymerase from the RNA-DNA complex.[4] In E. coli, one intrinsic termination signal consists of an RNA hairpin that has high amounts of guanine and cytosine, as well as a region high in uracil nucleobases.[4]
Factor-dependent terminators require proteins for proper termination.[4] One example is rho-dependent termination, a common termination mechanism found in bacteria that involves the binding of Rho protein to remove RNA polymerase from the DNA-RNA complex.[4]