Ubiqitin ligases and their activators Question 3 options: 1234 APC/C-activating subunit in all cells; triggers initial activation of APC/C at metaphase-to-anaphase transition; stimulated by M-CDK activity 1234 catalyzes ubiquitylation of regulatory proteins involved primarily in exit from mitosis, including securin and S- and M-cyclins; regulated by association with activating subunits 1234 catalyzes ubiquitylation of regulatory proteins involved in G1 control, including some CKls; phosphorylation of target protein usually required for its activity 1234 APC/C-activating subunit that maintains APC/C activity after anaphase and throughout G1; 1. APC/C 2. Cdc20 3. Cdh1 4. SCF