Start-specific transcription in yeast.

At the G1 to S transition of the budding yeast cell cycle there is burst of transcription of at least 30 different genes. This may in part be due to the fact that Saccheromyes cerevisiae often exists as a colonial micro-organism which spends most of its time in stationary phase (G0). When cells have the opportunity to enter the mitotic cell cycle, there is a selective advantage for cells that can start dividing rapidly and efficiently. Thus it is not surprising that they resynthesize enzymes critical for high-fidelity replication of DNA and replace other components that may not have survived extended G0 arrest. Proteins that are responsible for starting the cell cycle, particularly those that would disrupt the cycle if they were produced at other stages of the cell cycle, are transcribed specifically at the G1/S transition. Most of the G1 cyclins are expressed specifically at this time, and their activity determines the timing of the G1/S transition (Richardson et al. 1989; Nash et al. 1988; Cross 1988).