Much of the work on how the cell cycle is regulated has focused on Cyclin-Dependent Kinase (CDK)-mediated regulation of factors that control the coordinate expression of genes required for entry into the cell cycle. In Saccharomyces cerevisiae, SBF and MBF are related transcription factors that co-ordinately activate a large group of genes at the G1/S transition, and their activation depends on the Cln3-Cdk1 form of the cyclin-dependent kinase. However, cells are viable in the absence of Cln3, or SBF and MBF, indicating that other regulatory pathways must exist that activate the budding yeast cell cycle. The known CDK-independent pathways are made up of various phosphatases and plasma membrane transporters that control ion homeostasis in early G1 phase, a time when cells assess environmental growth conditions in order to commit to cell cycle entry. The enigmatic Bck2 protein is thought to act within these CDK-independent pathways, but the means by which it activates G1/S-regulated genes is not known. Bck2 contains little sequence homology to any known protein. In order to understand how CDK-independent pathways operate, I have studied the Bck2 protein using multiple approaches. In one approach, I have screened for novel SBF/MBF-binding proteins in order to determine if other non-CDK proteins, such as Bck2, might activate SBF and MBF. I have also investigated which region of Bck2 is required for its activity in order to determine if Bck2’s transcriptional activation region is essential. Using one of the iii truncation derivatives from this analysis, I have screened for proteins that interact with Bck2. One of these novel proteins is Mcm1, a global transcriptional activator of genes involved in cell cycle progression, mating gene transcription and metabolism. My studies suggest that Bck2 regulates the activity of Mcm1 in early G1 phase to activate the expression of SWI4, CLN3, and others. My evidence suggests that Bck2 competes for binding to a specific pocket on Mcm1 that is also bound by an Mcm1 repressor called Yox1. My findings suggest that CDK-independent pathways function through Bck2, in order to induce the initial suite of genes required for entry into the cell cycle.

Much of the work on how the cell cycle is regulated has focused on Cyclin-Dependent Kinase (CDK)-mediated regulation of factors that control the coordinate expression of genes required for entry into the cell cycle. In Saccharomyces cerevisiae, SBF and MBF are related transcription factors that co-ordinately activate a large group of genes at the G1/S transition, and their activation depends on the Cln3-Cdk1 form of the cyclin-dependent kinase. However, cells are viable in the absence of Cln3, or SBF and MBF, indicating that other regulatory pathways must exist that activate the budding yeast cell cycle. The known CDK-independent pathways are made up of various phosphatases and plasma membrane transporters that control ion homeostasis in early G1 phase, a time when cells assess environmental growth conditions in order to commit to cell cycle entry. The enigmatic Bck2 protein is thought to act within these CDK-independent pathways, but the means by which it activates G1/S-regulated genes is not known. Bck2 contains little sequence homology to any known protein. In order to understand how CDK-independent pathways operate, I have studied the Bck2 protein using multiple approaches. In one approach, I have screened for novel SBF/MBF-binding proteins in order to determine if other non-CDK proteins, such as Bck2, might activate SBF and MBF. I have also investigated which region of Bck2 is required for its activity in order to determine if Bck2’s transcriptional activation region is essential. Using one of the iii truncation derivatives from this analysis, I have screened for proteins that interact with Bck2. One of these novel proteins is Mcm1, a global transcriptional activator of genes involved in cell cycle progression, mating gene transcription and metabolism. My studies suggest that Bck2 regulates the activity of Mcm1 in early G1 phase to activate the expression of SWI4, CLN3, and others. My evidence suggests that Bck2 competes for binding to a specific pocket on Mcm1 that is also bound by an Mcm1 repressor called Yox1. My findings suggest that CDK-independent pathways function through Bck2, in order to induce the initial suite of genes required for entry into the cell cycle.