Cotranslationale

Cotranslationale, often rendered cotranslational in English, describes biological processes that occur simultaneously with the translation of mRNA by ribosomes. The term is used to distinguish events that take place as a nascent polypeptide is being synthesized from those that occur after translation is complete. Cotranslationale processes are central to how many proteins are folded, targeted, and edited as they emerge from the ribosome.

Cotranslational folding refers to the initial folding steps that begin while the polypeptide is still attached to the ribosome. Nascent chains interact with ribosome-associated chaperones and factors that influence folding pathways and help prevent misfolding. In eukaryotes, cytosolic chaperone systems such as Hsp70 assist nascent chains, while bacterial systems use factors like Trigger Factor.

Cotranslational targeting and translocation describe how some nascent chains are guided to membranes or organelles during synthesis. In eukaryotes, signal peptides are recognized by the signal recognition particle (SRP), which pauses translation and routes the ribosome-nascent chain complex to the endoplasmic reticulum. The polypeptide then translocates through or integrates into the Sec61 translocon.

Cotranslational quality control encompasses mechanisms that monitor ribosome activity during translation. When stalls or collisions occur, ribosome-associated quality control pathways can ubiquitinate and degrade incomplete nascent chains to maintain proteome integrity.

Cotranslational modifications can also begin during translation. For example, N-linked glycosylation often initiates cotranslationally in the ER lumen as polypeptides are threaded into the ER. Overall, cotranslationale processes shape protein folding, targeting, and quality control from the moment of synthesis.