Molecular function

protein tag, ubiquitin-like protein modifier

A molecular function exhibited by a protein that is covalently attached (AKA tagged or conjugated) to another protein where it acts as a marker, recognized by the cellular apparatus to target the tagged protein for some cellular process such as modification, sequestration, transport or degradation.

protein tagging activity, ubiquitin

Use this term to annotate conjugated tags, not for conjugating enzymes. At the time of writing, all known gene products with this activity are ubiquitin-like, either based on overall sequence similarity or the presence of common motifs and structures.