Termination signal
A termination signal is a sequence that signals the end of
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]
Bacterial Termination Signals
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]
Antitermination
Antitermination involves the inhibition of signal terminators.[4] RNA polymerase is prevented from detaching from the RNA in response to a termination signal, increasing downstream gene expression.[4]
Antitermination can occur in a variety of ways.[4] Some antiterminators disrupt termination signals by inhibiting RNA hairpin generation, while other antiterminators are proteins that bind to RNA polymerase and cause RNA polymerase to continue transcription past termination signals.[4] Depending on the environment of the cell, antitermination may be crucial to cell survival.[4] These antitermination mechanisms are crucial when the cell is under stress, allowing for increased expression of downstream genes that are needed under dire circumstances.[4]
Termination Signal Efficiency
Transcription
Termination efficiency of
Translation
In translation, termination efficiency is dependent on the context of the termination signal (stop codon).[2] Traditionally, the termination signal for translation is a 3 nucleobase sequence called a stop codon.[2] Research has shown that the nucleobases surrounding the stop codon can impact termination efficiency.[2] Specifically, the 4th base (nucleobase directly following the stop codon) has a significant impact on the termination efficiency.[2] In particular, when the nucleobase at the 4th position is a purine (adenine or guanine), termination efficiency is improved.[2] Pyrimidines (cytosine or uracil) in the 4th position result in lower termination efficiency.[2] It has been found that highly expressed genes have higher termination efficiency due to the presence of a purine in the 4th position.[2]
References
- ^ ISBN 978-0-323-07446-9, retrieved 15 October 2021
- ^ PMID 7777525.
- ^ S2CID 5263873.
- ^ PMID 21478900.
- Merrill, Dr. Gary F. 'Transcription', lecture notes distributed in Biochemistry 451 General Biochemistry, Oregon State University, Weigend on 6 June 2006.