Candida albicans is a ubiquitous opportunistic pathogen that is the most prevalent cause of hospital-acquired fungal infections. In mammalian hosts, C. albicans is engulfed by phagocytes that attack the pathogen with DNA-damaging reactive oxygen species (ROS). Acetylation of histone H3 lysine 56 (H3K56) by the fungal-specific histone acetyltransferase Rtt109 is important for yeast model organisms to survive DNA damage and maintain genome integrity. To assess the importance of Rtt109 for C. albicans pathogenicity, we deleted the predicted homolog of Rtt109 in the clinical C. albicans isolate, SC5314. C. albicans rtt109 −/− mutant cells lack acetylated H3K56 (H3K56ac) and are hypersensitive to genotoxic agents. Additionally, rtt109 −/− mutant cells constitutively display increased H2A S129 phosphorylation and elevated DNA repair gene expression, consistent with endogenous DNA damage. Importantly, C. albicans rtt109 −/− cells are significantly less pathogenic in mice and more susceptible to killing by macrophages in vitro than are wild-type cells. Via pharmacological inhibition of the host NADPH oxidase enzyme, we show that the increased sensitivity of rtt109 −/− cells to macrophages depends on the host's ability to generate ROS, providing a mechanistic link between the drug sensitivity, gene expression, and pathogenesis phenotypes. We conclude that Rtt109 is particularly important for fungal pathogenicity, suggesting a unique target for therapeutic antifungal compounds.acetylation | chromatin | fungal pathogenesis | DNA damage resistance | macrophage

Accurate chromosome segregation is dependent on the centromere-specific histone H3 isoform known generally as CenH3, or as Cse4 in budding yeast. Cytological experiments have shown that Cse4 appears at extracentromeric loci in yeast cells deficient for both the CAF-1 and HIR histone H3/H4 deposition complexes, consistent with increased nondisjunction in these double mutant cells. Here, we examined molecular aspects of this Cse4 mislocalization. Genome-scale chromatin immunoprecipitation analyses demonstrated broader distribution of Cse4 outside of centromeres in cac1D hir1D double mutant cells that lack both CAF-1 and HIR complexes than in either single mutant. However, cytological localization showed that the essential inner kinetochore component Mif2 (CENP-C) was not recruited to extracentromeric Cse4 in cac1D hir1D double mutant cells. We also observed that rpb1-1 mutants displayed a modestly increased Cse4 half-life at nonpermissive temperatures, suggesting that turnover of Cse4 is partially dependent on Pol II transcription. We used genome-scale assays to demonstrate that the CAF-1 and HIR complexes independently stimulate replication-independent histone H3 turnover rates. We discuss ways in which altered histone exchange kinetics may affect eviction of Cse4 from noncentromeric loci.

The histone acetyltransferase Rtt109 is the sole enzyme responsible for acetylation of histone H3 lysine 56 (H3K56) in fungal organisms. Loss of Rtt109 renders fungal cells extremely sensitive to genotoxic agents, and prevents pathogenesis in several clinically important species. Here, via a high throughput chemical screen of >300,000 compounds, we discovered a chemical inhibitor of Rtt109 that does not inhibit other acetyltransferase enzymes. This compound inhibits Rtt109 regardless of which histone chaperone cofactor protein (Asf1 or Vps75) is present, and appears to inhibit Rtt109 via a tight-binding, uncompetitive mechanism.

Candida albicans is the most prevalent human fungal pathogen. To successfully propagate an infection, this organism relies on the ability to change morphology, express virulence-associated genes and resist DNA damage caused by the host immune system. Many of these events involve chromatin alterations that are crucial for virulence. This review will focus on the studies that have been conducted on how chromatin function affects pathogenicity of C. albicans and other fungi. This article is part of a Special Issue entitled: Histone chaperones and Chromatin assembly

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