Destruction Box in Cyclins (a) Mitotic cyclin destruction box COOH Cyclin A Arg-Thr-Val-Leu-Gly-Val-lle-Gly-Asp Cyclin B1 Arg-Thr-Ala-Leu-Gly-Asp-lle-Gly-Asn Cyclin B2 Arg-Ala-Ala-Leu-Gly-Glu-lle-Gly-Asn (b) Polyubiquitination of mitotic cyclin APC (E3) Proteasome Degraded cyclin peptides P夏TAs0M n E2- n E2 n nE1-、 UbiquitinDestruction Box in Cyclins