Transcriptional repressor at START; binds to SBF (Swi4p-Swi6p) at SCB promoter elements in G1 to repress transcription; START inhibitor that retains Cdc28-Cln3 at the ER; acts with Ydj1p to promote release of the complex in a growth-mediated positive feedback loop to trigger START; unstable and degraded by SCF-Grr1 after phosphorylation; contains a G1/S transcription factor binding (GTB) motif; binds SBF-regulated promoters in HU-treated cells; substrate of Cdc28p and Pho85p; hyperphosphorylated