Multiple SWI6-dependent cis-acting elements control SWI4 transcription through the cell cycle

Area of Science:

• Molecular Biology
• Yeast Genetics
• Cell Cycle Regulation

Background:

• The SWI4 gene in Saccharomyces cerevisiae is essential for cell cycle control at the G1/S transition.
• SWI4 transcription is cell cycle-regulated, a crucial feature for regulating other cell cycle genes.
• Understanding SWI4 regulation is key to comprehending normal cell cycle progression.

Purpose of the Study:

• To identify and characterize the cis- and trans-acting regulatory elements controlling SWI4 gene transcription.
• To elucidate the role of MluI cell cycle boxes (MCBs) and the SWI6 protein in SWI4 regulation.

Main Methods:

• Deletion analysis of the SWI4 promoter region.
• Mutation analysis of SWI6.
• Quantification of SWI4 mRNA levels in various mutant strains and conditions.

Main Results:

• A 140-bp region of the SWI4 promoter acts as a cell cycle-regulated upstream activating sequence (UAS).
• Deletion of three MluI cell cycle boxes (MCBs) reduced SWI4 mRNA by 10-fold but did not abolish periodicity.
• SWI6 mutations abolished SWI4 transcription periodicity, indicating its essential role, while MCBs contribute but are not solely responsible.

Conclusions:

• SWI4 transcription is regulated by both MCBs and at least one other SWI6-dependent element.
• SWI6 is critical for both the activation and repression of SWI4 transcription throughout the cell cycle.
• An alternative pathway, possibly involving MCBs, can activate SWI4 transcription independently of SWI6.