G1/S-specific cyclin essential for the control of the cell cycle at the G1/S (start) transition. CLN3 may be an upstream activator of the G1 cyclins which directly catalyze start. Required for budding and for cell cycle progression and morphogenesis in environment-induced hyphae. Degradation is mediated by GRR1. Through binding to CDC28, controls the phosphorylation of SLA1 which regulates cortical actin patch dynamics. Interacts with CDC28 and SLA1. Repressed by farnesol. Hyperphosphorylated. GRR1 preferentially mediates the degradation of hyperphosphorylated CLN3. Belongs to the cyclin family.