Termination

Term in genetics. Termination, from Latin terminatio = limitation, chain termination, chain termination. In genetics, termination refers to the third and final stage of translation, transcription and replication - after initiation and elongation.

The signal structures that trigger termination during DNA synthesis (replication) are still largely unknown. - There are various possibilities for the termination of bacterial RNA synthesis (transcription): GC-rich, inverted repeats and 3'-terminally adjacent A/T-rich sections on the template DNA act as terminators. On the corresponding RNA transcript, the inverted repeats form a hairpin loop that blocks the activity of the RNA polymerase, and 3'-terminal U/A pairings create an unstable RNA-DNA hybrid segment that promotes the detachment of the RNA from the DNA template.

Some transcripts can only be terminated with the help of special proteins (transcriptional termination factors), such as the RNA-binding rho factor (Rho protein).

In the case of linear DNA - such as in the chromosomes of eukaryotes - termination does not need to be specifically triggered, as replication is automatically terminated when two replication forks meet or the DNA ends.

For RNA polymerase III, the simple sequence TTTT (e.g. at the 3' end of 5S rRNA genes) is sufficient. It is too short to form a secondary structure, so that it is irrelevant here - in contrast to bacterial RNA termination.

The detachment of the respective polymerase from the DNA and the release of the transcript are probably dependent on additional DNA- or RNA-(transcript)-binding factors in all eukaryotic RNA polymerases. - Termination during protein synthesis (translation) is signaled by the termination codons (stop codon) UAA, UAG and UGA in interaction with special proteins (translational termination factors, releasing factors).