Substrate and inhibitor of the cyclin-dependent protein kinase CDC28. Its activity could be important for faithful segregation of chromosomes to daughter cells. It acts in response to a signal from a post-start checkpoint. Interacts with HOG1. Phosphorylated by cyclin-dependent kinases CDC28 and PHO85 in association with G1-cyclins, promoting degradation of SIC1 and exit form G1. May contain a covalently attached chromophore. The N-terminus is blocked. Present with 768 molecules/cell in log phase SD medium.