A chemical‐genetic screen to unravel the genetic network of CDC28/CDK1 links ubiquitin and Rad6–Bre1 to cell cycle progression

Abstract

Cyclin‐dependent kinases (CDKs) control the eukaryotic cell cycle, and a single CDK, Cdk1 (also known as Cdc28), is necessary and sufficient for cell cycle regulation in the budding yeast Saccharomyces cerevisiae. Cdk1 regulates cell cycle‐dependent processes such as transcription, DNA replication and repair, and chromosome segregation. To gain further insight into the functions of Cdk1, we performed a high‐throughput chemical‐genetic array (CGA) screen aimed at unraveling the genetic network of CDK1. We identified 107 genes that strongly genetically interact with CDK1. Although these genes serve multiple cellular functions, genes involved in cell cycle regulation, transcription, and chromosome metabolism were overrepresented. DOA1, which is involved in maintaining free ubiquitin levels, as well as the RAD6–BRE1 pathway, which is involved in transcription, displayed particularly strong genetic interactions with CDK1. We discovered that DOA1 is important for cell cycle entry by supplying ubiquitin. Furthermore, we found that the RAD6–BRE1 pathway functions downstream of DOA1/ubiquitin but upstream of CDK1, by promoting transcription of cyclins. These results link cellular ubiquitin levels and the Rad6–Bre1 pathway to cell cycle progression.