Terminator (genetics)

In molecular biology, a terminator is a section of nucleic acid sequence that marks the end of a gene or operon during transcription in bacteria and archaea. This sequence signals to RNA polymerase that transcription should cease.

The terminator sequence typically consists of inverted repeat sequences that form a stem-loop structure in the mRNA transcript, followed by a string of uracil (U) residues in bacteria. This structure destabilizes the binding of RNA polymerase to the DNA template, causing the polymerase to detach and release the newly synthesized mRNA molecule.

There are two main types of terminators in bacteria:

• Rho-independent terminators (intrinsic terminators): These terminators function without the aid of any additional protein factors. The stem-loop structure formed by the inverted repeats followed by the string of uracils is sufficient to cause termination.

• Rho-dependent terminators: These terminators require the Rho protein, a helicase, to terminate transcription. Rho binds to the mRNA and moves towards the RNA polymerase. When the polymerase pauses at the terminator sequence, Rho catches up and unwinds the DNA-RNA hybrid, causing termination.

Terminators are essential components of gene expression, ensuring that transcription stops at the correct location and preventing the production of non-functional or harmful transcripts. The efficiency of a terminator can influence the levels of gene expression. Strong terminators result in lower levels of transcript, while weak terminators allow for higher levels of transcript. In synthetic biology, terminator sequences are frequently used as control elements to regulate gene expression.