Biological process

PTM, post-translational amino acid modification, post-translational modification, posttranslational amino acid modification, posttranslational modification, posttranslational protein modification

The process of covalently altering one or more amino acids in a protein after the protein has been completely translated and released from the ribosome.

This term should only be used to annotate a protein modification process that occurs after the protein has been released from the ribosome, and is therefore strictly post-translational. Modification of a free protein (one not attached to a ribosome) and modification of a C-terminal residue are post-translational processes. Some protein modifications occur while the protein is still in the ribosome but before translation has been completed; these modification processes are considered co-translational and should not be annotated using this term.