The G1/S repressor WHI5 is expressed at similar levels throughout the cell cycle.

To address this question, we monitored single WHI5 mRNA molecules in single live cells using confocal microscopy, and quantified WHI5 mRNA copy number in G1, G1/S, and S/G2/M phase cells. We observed that WHI5 mRNA is found in very similar amount irrespective of cell cycle stage. The constant WHI5 mRNA copy number throughout G1 phase rules out alterations in mRNA abundance as a contributing factor for any putative dilution of Whi5.