ɪn ðɪs sˈɪstəm, ɐ smˈɔːl sˈɛvən ˈeɪt kˌeɪdˈiː pɹˈoʊtiːn kˈɔːld "jˈuːbɪkwˌɪtɪn" ɪz ɐfˈɪkst tʊ ɐ tˈɑːɹɡɪt pɹˈoʊtiːn, ænd ɪz ðɛɹbˈaɪ tˈɑːɹɡɪɾᵻd fɔːɹ dᵻstɹˈʌkʃən baɪ ɐ stɹˈʌktʃɚ kˈɔːld ðə "pɹˈoʊɾiəsˌʌm".
In this system, a small (7–8 kd)protein called "ubiquitin" is affixed to a target protein, and is thereby targeted for destruction by a structure called the "proteasome".