The protein Zwilch is an essential component of the mitotic checkpoint, which prevents cells from prematurely exiting mitosis. It is required for the assembly of the dynein-dynactin, Mad2 complexes and spindly/CG15415 onto kinetochores [, , ]. Zwilch is a component of the RZZ complex, which is composed of Rod, Zw10 and Zwilch.