The adherence of Candida glabrata to host cells is mediated, at least in part, by the EPA genes, a family of adhesins encoded at subtelomeric loci, where they are subject to transcriptional silencing. We show that normally silent EPA genes are expressed during murine urinary tract infection (UTI) and that the inducing signal is the limitation of nicotinic acid (NA), a precursor of nicotinamide adenine dinucleotide (NAD ⁺ ). C. glabrata is an NA auxotroph, and NA-induced EPA expression is likely the result of a reduction in NAD ⁺ availability for the NAD ⁺ -dependent histone deacetylase Sir2p. The adaptation of C. glabrata to the host, therefore, involves a loss of metabolic capacity and exploitation of the resulting auxotrophy to signal a particular host environment.

Candida glabrata is an important opportunistic pathogen causing both mucosal and bloodstream infections. C. glabrata is able to adhere avidly to mammalian cells, an interaction that depends on the Epa1p lectin. EPA1 is shown here to be a member of a larger family of highly related genes encoded in subtelomeric clusters. Subtelomeric clustering of large families of surface glycoprotein-encoding genes is a hallmark of several pathogens, including Plasmodium, Trypanosoma, and Pneumocystis. In these other pathogens, a single surface glycoprotein is expressed, whereas other genes in the family are transcriptionally silent. Similarly, whereas EPA1 is expressed in vitro, EPA2-5 are transcriptionally repressed. This repression is shown to be due to regional silencing of the subtelomeric loci. In Saccharomyces cerevisiae, subtelomeric silencing is initiated by Rap1p binding to the telomeric repeats and subsequent recruitment of the Sir complex by protein-protein interaction. We demonstrate here that silencing of the subtelomeric EPA loci also depends on functional Sir3p and Rap1p. This identification and analysis of the EPA gene family provides a compelling example in an ascomycete of chromatin-based silencing of natural subtelomeric genes and provides for the first time in a pathogen, molecular insight into the transcriptional silencing of large subtelomeric gene families.

SigmaE is an alternative sigma factor that controls the extracytoplasmic stress response in Escherichia coli. SigmaE is essential at high temperatures but was previously thought to be nonessential at temperatures below 37 degrees C. We present evidence that sigmaE is an essential sigma factor at all temperatures. Cells lacking sigmaE are able to grow at low temperatures because of the presence of a frequently arising, unlinked suppressor mutation.

Establishment of cohesion between sister chromatids is coupled to replication fork passage through an unknown mechanism. Here we report that TRF4 , an evolutionarily conserved gene necessary for chromosome segregation, encodes a DNA polymerase with β-polymerase–like properties. A double mutant in the redundant homologs, TRF4 and TRF5 , is unable to complete S phase, whereas a trf4 single mutant completes a presumably defective S phase that results in a failure of cohesion between the replicated sister chromatids. This suggests that TRF s are a key link in the coordination between DNA replication and sister chromatid cohesion. Trf4 and Trf5 represent the fourth class of essential nuclear DNA polymerases (designated DNA polymerase kappa) in Saccharomyces cerevisiae and probably in all eukaryotes.

We characterized the oxidative stress response of Candida glabrata to better understand the virulence of this fungal pathogen. C. glabrata could withstand higher concentrations of H ₂ O ₂ than Saccharomyces cerevisiae and even Candida albicans . Stationary-phase cells were extremely resistant to oxidative stress, and this resistance was dependent on the concerted roles of stress-related transcription factors Yap1p, Skn7p, and Msn4p. We showed that growing cells of C. glabrata were able to adapt to high levels of H ₂ O ₂ and that this adaptive response was dependent on Yap1p and Skn7p and partially on the general stress transcription factors Msn2p and Msn4p. C. glabrata has a single catalase gene, CTA1 , which was absolutely required for resistance to H ₂ O ₂ in vitro. However, in a mouse model of systemic infection, a strain lacking CTA1 showed no effect on virulence.