Abf1 Is an Essential Protein That Participates in Cell Cycle Progression and Subtelomeric Silencing in Candida glabrata

Accurate DNA replication and segregation is key to reproduction and cell viability in all organisms. Autonomously replicating sequence-binding factor 1 (Abf1) is a multifunctional protein that has essential roles in replication, transcription, and regional silencing in the model yeast Saccharomyces cerevisiae. In the opportunistic pathogenic fungus Candida glabrata, which is closely related to S. cerevisiae, these processes are important for survival within the host, for example, the regulation of transcription of virulence-related genes like those involved in adherence. Here, we describe that CgABF1 is an essential gene required for cell viability and silencing near the telomeres, where many adhesin-encoding genes reside. CgAbf1 mediated subtelomeric silencing depends on the 43 C-terminal amino acids. We also found that abnormal expression, depletion, or overexpression of Abf1, results in defects in nuclear morphology, nuclear segregation, and transit through the cell cycle. In the absence of ABF1, cells are arrested in G2 but start cycling again after 9 h, coinciding with the loss of cell viability and the appearance of cells with higher DNA content. Overexpression of CgABF1 causes defects in nuclear segregation and cell cycle progression. We suggest that these effects could be due to the deregulation of DNA replication.