Negative regulatory component of the MBF transcription factor complex involved in cell-cycle G1/S phase-specific gene expression and more particularly DNA replication checkpoint-dependent gene expression. Component of the MBF transcription factor complex. Expression is induced during S phase and depends on the MBF transcription factor complex. Phosphorylated in response to hydroxyurea. Phosphorylation inhibits the repressor activity and is dependent on rad3. However, the regulation of yox1 by rad3 is probably indirect.