Identification of genes of Aspergillus fumigatus up-regulated during growth on endothelial cells

Angiogenesis at the mold-host interface: a potential key to understanding and treating invasive aspergillosis

Invasive aspergillosis (IA) in neutropenic patients is characterized by angioinvasion, intravascular thrombosis and tissue infarction, features that lead to sequestration of infected tissue and impaired fungal clearance. Recent research has shown that host angiogenesis, the homeostatic compensatory response to tissue hypoxia, is downregulated by Aspergillus fumigatus secondary metabolites. A. fumigatus metabolites inhibit multiple key angiogenic mediators, notably basic FGF, VEGF and their respective receptors. Moreover, repletion of basic FGF and VEGF enhances angiogenesis at the site of infection, induces trafficking of polymorphonuclear leukocytes into fungal-infected tissue and enhances antifungal drug activity. This review summarizes the emerging roles of vasculopathy and angiogenesis in the pathogenesis of IA, emphasizing the importance of the underlying mode of immunosuppression. Modulation of angiogenesis is a potential target for novel therapeutic strategies against IA.

Substrate specifity profiling of the Aspergillus fumigatus proteolytic secretome reveals consensus motifs with predominance of Ile/Leu and Phe/Tyr

Background

The filamentous fungus Aspergillus fumigatus (AF) can cause devastating infections in immunocompromised individuals. Early diagnosis improves patient outcomes but remains challenging because of the limitations of current methods. To augment the clinician's toolkit for rapid diagnosis of AF infections, we are investigating AF secreted proteases as novel diagnostic targets. The AF genome encodes up to 100 secreted proteases, but fewer than 15 of these enzymes have been characterized thus far. Given the large number of proteases in the genome, studies focused on individual enzymes may overlook potential diagnostic biomarkers.

Methodology and Principal Findings

As an alternative, we employed a combinatorial library of internally quenched fluorogenic probes (IQFPs) to profile the global proteolytic secretome of an AF clinical isolate in vitro. Comparative protease activity profiling revealed 212 substrate sequences that were cleaved by AF secreted proteases but not by normal human serum. A central finding was that isoleucine, leucine, phenylalanine, and tyrosine predominated at each of the three variable positions of the library (44.1%, 59.1%, and 57.0%, respectively) among substrate sequences cleaved by AF secreted proteases. In contrast, fewer than 10% of the residues at each position of cleaved sequences were cationic or anionic. Consensus substrate motifs were cleaved by thermostable serine proteases that retained activity up to 50°C. Precise proteolytic cleavage sites were reliably determined by a simple, rapid mass spectrometry-based method, revealing predominantly non-prime side specificity. A comparison of the secreted protease activities of three AF clinical isolates revealed consistent protease substrate specificity fingerprints. However, secreted proteases of A. flavus, A. nidulans, and A. terreus strains exhibited striking differences in their proteolytic signatures.

Conclusions

This report provides proof-of-principle for the use of protease substrate specificity profiling to define the proteolytic secretome of Aspergillus fumigatus. Expansion of this technique to protease secretion during infection could lead to development of novel approaches to fungal diagnosis.

Shaping the fungal adaptome--stress responses of Aspergillus fumigatus

Aspergillus fumigatus as prime pathogen to cause aspergillosis has evolved as a saprophyte, but is also able to infect and colonise immunocompromised hosts. Based on the 'dual use' hypothesis of fungal pathogenicity, general characteristics have to be considered as unspecific virulence determinants, among them stress adaptation capacities. The susceptible, warm-blooded mammalian host represents a specific ecological niche that poses several kinds of stress conditions to the fungus during the course of infection. Detailed knowledge about the cellular pathways and adaptive traits that have evolved in A. fumigatus to counteract situations of stress and varying environmental conditions is crucial for the identification of novel and specific antifungal targets. Comprehensive profiling data accompanied by mutant analyses have shed light on such stressors, and nutritional deprivation, oxidative stress, hypoxia, elevated temperature, alkaline pH, extensive secretion, and, in particular during treatment with antifungals, cell membrane perturbations appear to represent the major hazards A. fumigatus has to cope with during infection. Further efforts employing innovative approaches and advanced technologies will have to be made to expand our knowledge about the scope of the A. fumigatus adaptome that is relevant for disease.

Divergent Protein Kinase A isoforms co-ordinately regulate conidial germination, carbohydrate metabolism and virulence in Aspergillus fumigatus

The genome of Aspergillus fumigatus encodes two isoforms of the catalytic subunit of the cAMP-dependent Protein Kinase (PKA). Although deletion of the class I isoform, pkaC1, leads to an attenuation of virulence, the function of the class II subunit, PkaC2, was previously uninvestigated. In this report, we demonstrate that both isoforms act in concert to support various physiologic processes that promote the virulence of this pathogen. Whereas pkaC1 and pkaC2 single-deletion mutants display wild-type conidial germination, a double-deletion mutant is delayed in germination in response to environmental nutrients. Furthermore, PkaC1 and PkaC2 interact to positively regulate flux through the carbohydrate catabolic pathway and, consequently, the ΔpkaC1ΔpkaC2 mutant is unable to grow on low glucose concentrations. Importantly, the reduced germinative capacity and inability to utilize glucose observed for the ΔpkaC1ΔpkaC2 strain correlated with an inability of the mutant to establish infection in a murine model. Conversely, overexpression of pkaC2 both promotes the in vitro growth on glucose, and restores the fungal burden and mortality associated with the ΔpkaC1 to that of the wild-type organism. Taken together, these data demonstrate the functional capacity of pkaC2 and emphasize the importance of PKA-mediated metabolic control in the pathogenic potential of A. fumigatus.

Polarized response of endothelial cells to invasion by Aspergillus fumigatus

Hyphal invasion of blood vessels is a prominent feature of invasive aspergillosis. During invasive pulmonary aspergillosis, Aspergillus fumigatus hyphae invade the abluminal endothelial cell surface, whereas they invade the luminal endothelial cell surface during haematogenous dissemination. We investigated the endothelial cell response to abluminal and luminal infection with A. fumigatus hyphae in vitro. We found that these hyphae invaded the abluminal endothelial cell surface without inducing the formation of endothelial cell pseudopods. Also, the internalized hyphae were surrounded by a loose network of microfilaments. In contrast, A. fumigatus hyphae invaded the luminal endothelial cell surface by inducing by the formation of endothelial cell pseudopods. These endocytosed hyphae were surrounded by a tight network of microfilaments. Abluminal infection induced greater E-selectin, IL-8, tissue factor and TNF-alpha gene expression, but less endothelial cell damage than did luminal infection. Endothelial cell stimulation by infection of either surface was mediated by endothelial cell-derived TNF-alpha, and was not influenced by gliotoxin secreted by A. fumigatus. These differences in the endothelial cell response to abluminal versus luminal infection may contribute to differences in the pathogenesis of invasive versus haematogenously disseminated aspergillosis.

Deletion of the regulatory subunit of protein kinase A in Aspergillus fumigatus alters morphology, sensitivity to oxidative damage, and virulence

Aspergillus fumigatus is an important opportunistic fungal pathogen. The cAMP-dependent protein kinase (PKA) signaling pathway plays an important role in regulating morphology, growth, and virulence in a number of fungal pathogens of plants and animals. We have constructed a mutant of A. fumigatus that lacks the regulatory subunit of PKA, pkaR, and analyzed the growth and development, sensitivity to oxidative damage, and virulence of the mutant, along with those of the wild type and a complemented mutant. Both growth and germination rates of the mutant are reduced, and there are morphological abnormalities in conidiophores, leading to reduced conidiation. Conidia from the DeltapkaR mutant are more sensitive to killing by hydrogen peroxide, menadione, paraquat, and diamide. However, the hyphae of the mutant are killed to a greater extent only by paraquat and diamide, whereas they are less susceptible to the effects of hydrogen peroxide. In an immunosuppressed mouse model, intranasally administered conidia of the mutant are significantly less virulent than those of the wild type or a complemented mutant. Unregulated PKA signaling is detrimental to the virulence of A. fumigatus, perhaps through the reduced susceptibility of the mutant to damage by oxidizing agents and reduced growth kinetics.

Genomics of Aspergillus fumigatus

Aspergillus fumigatus is a filamentous fungal saprophyte that is ubiquitous in the environment. It is also a human pathogen and induces allergenic response, negatively impacting health care and associated costs significantly around the world. Much of the basic biology of this organism is only poorly understood, but the recent completion and publication of its genome sequence provides an excellent tool for researchers to gain insight into these processes. In this review we will summarize some of the more salient features revealed by analysis of the genome, including the search for candidate pathogenicity genes and the switch to a pathogenic lifestyle, allergen proteins, DNA repair, secondary metabolite gene clusters that produce compounds both useful and toxic, a theoretical capability of this asexual organism to reproduce sexually, signalling, and transcription. A. fumigatus was compared with the food biotechnology fungus Aspergillus oryzae and sexual fungus Aspergillus nidulans, as well as other fungi, in an attempt to discern key differences between these organisms.

Expression of Aspergillus fumigatus virulence-related genes detected in vitro and in vivo with competitive RT-PCR

We have measured the transcription of several genes that have been implicated as virulence factors in Aspergillus fumigatus, including fos-1, a histidine kinase, two-component signal protein, rhbA, a ras-related protein required for signaling, pksP, a polyketide synthase involved in biosynthesis of melanin, pabA synthetase, an enzyme catalyzing a late step in the biosynthesis of folate, lysF, a homoconitase related to lysine biosynthesis, and cpcA, the transcriptional activator of the cross-pathway control system of amino acid biosynthesis. Transcription levels were determined from in vitro grown organism as well as from lung tissue from mice infected with A. fumigatus. Our data indicate that fos-1 and rhbA transcription increased significantly during the infection in mice, compared to the other genes whose transcription remained the same (pksP, cpcA, pabA) or decreased slightly (lysF). In vitro measurements of transcription compared to transcription in infected lung tissue demonstrated low levels of fos-1 and rhbA, 20-40-fold increases (cpcA, lysF, pabA), while pksP was not detected from cultures. Our data demonstrate that transcription of these genes differs in vitro versus during disease.

Aspergillus fumigatus: Growth and virulence

Aspergillus fumigatus is a ubiquitous fungus that plays an important role in carbon and nitrogen recycling in nature. Because A. fumigatus is thermotolerant, it is a predominant organism during the high-temperature phase of the compost cycle. The ability to grow at elevated temperatures and to utilize numerous varied sources of both carbon and nitrogen to support its growth have made A. fumigatus an important opportunistic pathogen of humans as well as a vital part of the nutrient-recycling ecosystem. Data correlating the growth rate and germination potential of A. fumigatus at 37 degrees C with its pathogenic potential suggest that these are related, both when viewed from a population standpoint and when analyzed on a single gene basis. Nutritional versatility has been cited as an important contributor to virulence as well. Indeed, perturbation of pathways involved with nitrogen or carbon sensing has been shown to reduce virulence in animal models, even when in vitro growth rates have not been altered. Therefore, the remarkable ability of A. fumigatus to grow efficiently under a variety of environmental conditions and to utilize a wide variety of substrates to meet its nutritional needs contributes to its role as the predominant mould pathogen of immunocompromised patients.

Markers for host-induced gene expression in Trichophyton dermatophytosis

Dermatophytes are adapted to infect keratinized tissues by their ability to utilize keratin as a nutrient source. Although there have been numerous reports that dermatophytes like Trichophyton sp. secrete proteolytic enzymes, virtually nothing is known about the patterns of gene expression in the host or even when the organisms are cultured on protein substrates in the absence of a host. We characterized the expression of an aminopeptidase gene, the Trichophyton mentagrophytes homolog of the Trichophyton rubrum Tri r 4 gene. The T. rubrum gene was originally isolated based on the ability of the protein encoded by it to induce immediate and delayed-type hypersensitivity in skin tests. T. mentagrophytes Tri m 4 is closely related to Tri r 4 (almost 94% identity at the protein level). Tri m 4 resembles other protease-encoding genes thought to be virulence factors (for example, DPP V of Aspergillus fumigatus). The Tri m 4 protein was detected immunochemically both in fungal extracts and in the culture medium. Expression of the Tri m 4 gene was induced severalfold when T. mentagrophytes was grown on keratin and elastin. Ex vivo, strong induction was observed after culture on blood plasma, but the use of homogenized skin did not result in a significant increase in Tri m 4 transcript levels. In order to identify additional genes encoding putative virulence factors, differential cDNA screening was performed. By this method, a fungal thioredoxin and a cellulase homolog were identified, and both genes were found to be strongly induced by skin extracellular matrix proteins. Induction by superficial (keratin) and deep (elastin) skin elements suggests that the products of these genes may be important in both superficial and deep dermatophytosis, and models for their function are proposed. Upregulation of several newly identified T. mentagrophytes genes on protein substrates suggests that these genes encode proteins which are relevant to the dermatophyte-skin interaction.

Interaction of pathogenic fungi with host cells: Molecular and cellular approaches

This review provides an overview of several molecular and cellular approaches that are likely to supply insights into the host-fungus interaction. Fungi present intra- and/or extracellular host-parasite interfaces, the parasitism phenomenon being dependent on complementary surface molecules. The entry of the pathogen into the host cell is initiated by the fungus adhering to the cell surface, which generates an uptake signal that may induce its cytoplasmatic internalization. Furthermore, microbial pathogens use a variety of their surface molecules to bind to host extracellular matrix (ECM) components to establish an effective infection. On the other hand, integrins mediate the tight adhesion of cells to the ECM at sites referred to as focal adhesions and also play a role in cell signaling. The phosphorylation process is an important mechanism of cell signaling and regulation; it has been implicated recently in defense strategies against a variety of pathogens that alter host-signaling pathways in order to facilitate their invasion and survival within host cells. The study of signal transduction pathways in virulent fungi is especially important in view of their putative role in the regulation of pathogenicity. This review discusses fungal adherence, changes in cytoskeletal organization and signal transduction in relation to host-fungus interaction.

Genes and molecules involved in Aspergillus fumigatus virulence

Aspergillus fumigatus causes a wide range of diseases that include mycotoxicosis, allergic reactions and systemic diseases (invasive aspergillosis) with high mortality rates. Pathogenicity depends on immune status of patients and fungal strain. There is no unique essential virulence factor for development of this fungus in the patient and its virulence appears to be under polygenetic control. The group of molecules and genes associated with the virulence of this fungus includes many cell wall components, such as beta-(1-3)-glucan, galactomannan, galactomannanproteins (Afmp1 and Afmp2), and the chitin synthetases (Chs; chsE and chsG), as well as others. Some genes and molecules have been implicated in evasion from the immune response, such as the rodlets layer (rodA/hyp1 gene) and the conidial melanin-DHN (pksP/alb1 gene). The detoxifying systems for Reactive Oxygen Species (ROS) by catalases (Cat1p and Cat2p) and superoxide dismutases (MnSOD and Cu, ZnSOD), had also been pointed out as essential for virulence. In addition, this fungus produces toxins (14 kDa diffusible substance from conidia, fumigaclavin C, aurasperon C, gliotoxin, helvolic acid, fumagilin, Asp-hemolysin, and ribotoxin Asp fI/mitogilin F/restrictocin), allergens (Asp f1 to Asp f23), and enzymatic proteins as alkaline serin proteases (Alp and Alp2), metalloproteases (Mep), aspartic proteases (Pep and Pep2), dipeptidyl-peptidases (DppIV and DppV), phospholipase C and phospholipase B (Plb1 and Plb2). These toxic substances and enzymes seems to be additive and/or synergistic, decreasing the survival rates of the infected animals due to their direct action on cells or supporting microbial invasion during infection. Adaptation ability to different trophic situations is an essential attribute of most pathogens. To maintain its virulence attributes A. fumigatus requires iron obtaining by hydroxamate type siderophores (ornitin monooxigenase/SidA), phosphorous obtaining (fos1, fos2, and fos3), signal transductional falls that regulate morphogenesis and/or usage of nutrients as nitrogen (rasA, rasB, rhbA), mitogen activated kinases (sakA codified MAP-kinase), AMPc-Pka signal transductional route, as well as others. In addition, they seem to be essential in this field the amino acid biosynthesis (cpcA and homoaconitase/lysF), the activation and expression of some genes at 37 degrees C (Hsp1/Asp f12, cgrA), some molecules and genes that maintain cellular viability (smcA, Prp8, anexins), etc. Conversely, knowledge about relationship between pathogen and immune response of the host has been improved, opening new research possibilities. The involvement of non-professional cells (endothelial, and tracheal and alveolar epithelial cells) and professional cells (natural killer or NK, and dendritic cells) in infection has been also observed. Pathogen Associated Molecular Patterns (PAMP) and Patterns Recognizing Receptors (PRR; as Toll like receptors TLR-2 and TLR-4) could influence inflammatory response and dominant cytokine profile, and consequently Th response to infec tion. Superficial components of fungus and host cell surface receptors driving these phenomena are still unknown, although some molecules already associated with its virulence could also be involved. Sequencing of A. fumigatus genome and study of gene expression during their infective process by using DNA microarray and biochips, promises to improve the knowledge of virulence of this fungus.

Correlation betweenin vitrogrowth rate andin vivovirulence inAspergillus fumigatus

We describe a kinetic microbroth method of measuring the growth rate of Aspergillus fumigatus spectrophotometrically. Using this method, growth rates were determined for nine A. fumigatus isolates for which an LD90 value in immunosuppressed CD-1 mice had previously been obtained. Comparison of the growth rates and LD90 values of these isolates suggests that a correlation exists between the two parameters.

cAMP signaling in Aspergillus fumigatus is involved in the regulation of the virulence gene pksP and in defense against killing by macrophages

Aspergillus fumigatus is an important pathogen of immunocompromised hosts, causing pneumonia and invasive disseminated disease and resulting in high mortality. In order to determine the importance of the cAMP signaling pathway for virulence, three genes encoding putative elements of the pathway have been cloned and characterized: the adenylate cyclase gene acyA, and gpaA and gpaB, both of which encode alpha subunits of heterotrimeric G proteins. The acyA and gpaB genes were each deleted in A. fumigatus. Both mutants showed reduced conidiation, with the deltaacyA mutant producing very few conidia. The growth rate of the deltaacyA mutant was also reduced, in contrast to that of the deltagpaB mutant. Addition of 10 mM dibutyryl-cAMP to the culture medium completely restored the wild-type phenotype in both mutant strains. To study the influence of GPAB on the expression of the gene pksP, which encodes a virulence factor that is involved in pathogenicity, a pksPp-lacZ gene fusion was generated and integrated as a single copy at the pyrG gene locus of both the parental strain and the deltagpaB mutant strain. The deltagpaB mutant showed reduced expression of the pksPp-lacZ reporter gene relative to that in the parental strain. In mycelia of both the parental strain and the deltagpaB mutant pksPp-lacZ expression was increased when isobutyl-methyl-xanthine, an inhibitor of intracellular phosphodiesterases, was added to the medium. The survival rate of conidia after ingestion by human monocyte-derived macrophages was also determined. The killing rate for conidia from deltaacyA and deltagpaB strains was significantly higher than that for wild-type conidia. Taken together, these findings suggest that cAMP triggers a system that protects A. fumigatus from the effects of immune effector cells of the host.

Deletion of the Aspergillus fumigatus gene encoding the Ras-related protein RhbA reduces virulence in a model of Invasive pulmonary aspergillosis

Aspergillus fumigatus is the predominant mold pathogen in patients who lack functional innate immunity. The A. fumigatus rhbA gene was first identified as a transcript that was upregulated when the organism was grown in the presence of mammalian cells. To gain insight into the function of rhbA in the growth and pathogenesis of A. fumigatus, we constructed a strain that lacks a functional rhbA gene. The Delta rhbA mutant showed a significant reduction in virulence compared to the virulence of the wild type in a mouse model of invasive aspergillosis. Complementation of the deletion with the wild-type gene restored full virulence. Although the Delta rhbA mutant grew as well as the wild type on solid medium containing the rich nitrogen source ammonium, the growth of the mutant was impaired on medium containing poor nitrogen sources. Like the Saccharomyces cerevisiae rhb1 mutant, the Delta rhbA mutant exhibited increased uptake of arginine. In addition, the Delta rhbA strain underwent asexual development in submerged cultures, even under ammonium-excess conditions. Growth of the mutant with poor nitrogen sources eliminated both the arginine uptake and submerged asexual development phenotypes. The mutant showed enhanced sensitivity to the TOR kinase inhibitor rapamycin. These findings establish the importance of rhbA for A. fumigatus virulence and suggest a role for rhbA in nutrient sensing.

Biosynthesis of fungal melanins and their importance for human pathogenic fungi

For more than 40 years fungi have been known to produce pigments known as melanins. Predominantly these have been dihydroxyphenylalanine (DOPA)-melanin and dihydroxynaphthalene (DHN)-melanin. The biochemical and genetical analysis of the biosynthesis pathways have led to the identification of the genes and corresponding enzymes of the pathways. Only recently have both these types of melanin been linked to virulence in some human pathogenic and phytopathogenic fungi. The absence of melanin in human pathogenic and phytopathogenic fungi often leads to a decrease in virulence. In phytopathogenic fungi such as Magnaporthe grisea and Colletotrichum lagenarium, besides other possible functions in pathogenicity, DHN-melanin plays an essential role in generating turgor for plant appressoria to penetrate plant leaves. While the function of melanin in human pathogenic fungi such as Cryptococcus neoformans, Wangiella dermatitidis, Sporothrix schenckii, and Aspergillus fumigatus is less well defined, its role in protecting fungal cells has clearly been shown. Specifically, the ability of both DOPA- and DHN-melanins to quench free radicals is thought to be an important factor in virulence. In addition, in several fungi the production of fungal virulence factors, such as melanin, has been linked to a cAMP-dependent signaling pathway. Many of the components involved in the signaling pathway have been identified.

Cloning and expression of pkaC and pkaR, the genes encoding the cAMP-dependent protein kinase of Aspergillus fumigatus

This report describes the cloning and expression of both subunits of PKA in the opportunistic fungal pathogen Aspergillus fumigatus. The predicted translation product of the regulatory subunit, pkaR, is defined as a type II regulatory subunit. The gene encoding the A. fumigatus catalytic subunit, pkaC, contains the conserved kinase and activation domains that are characteristic of PkaC proteins. Both subunit mRNAs are expressed throughout the asexual life cycle of A. fumigatus. Message levels of pkaR and pkaC are higher during co-cultivation with alveolar epithelial cells than during culture alone.

Expression of the Aspergillus fumigatus rheb homologue, rhbA, is induced by nitrogen starvation

A gene encoding a ras protein with homology to the rheb family was cloned from Aspergillus fumigatus. Although conserved ras domains are present, the predicted RhbA protein sequence deviates from the ras consensus in a manner that is characteristic of rheb proteins. The invariant Gly-Gly in the first GTP-binding domain of ras proteins is replaced by Arg-Ser in RhbA, and a conserved Asp in the effector region of ras proteins is replaced by Asn in RhbA. The rhbA mRNA was detected throughout the A. fumigatus asexual developmental cycle, and accumulated over 5-fold in response to nitrogen starvation. The rhbA gene was able to complement the canavanine hypersensitivity of Saccharomyces cerevisiae Deltarhb1 mutants, suggesting that the two proteins share overlapping function.

cAMP alteration of growth rate of Aspergillus fumigatus and Aspergillus niger is carbon-source dependent

cAMP signalling has been shown to be essential for normal growth, morphology and virulence in fungal pathogens of both plants and animals. The effects of exogenous cAMP on the growth of the opportunistic pathogen Aspergillus fumigatus were compared to those of Aspergillus niger, which has previously been demonstrated to respond to extracellular cAMP. Both cAMP and phosphodiesterase inhibitors markedly reduced the radial growth rate of A. niger after 48 h on minimal medium with glucose as the carbon source, whereas the growth of A. fumigatus was not affected by cAMP. However, when glycerol, which does not initiate carbon catabolite repression, was used as a carbon source, cAMP inhibited the radial growth rate of only A. fumigatus (P<0.05). The addition of cAMP to glycerol-minimal medium resulted in a fourfold increase in protein kinase A activity in A. fumigatus cell extracts when compared with pre-treatment samples. The protein kinase A activity in A. fumigatus cell extracts from cultures grown in glucose did not change significantly with the addition of cAMP. These studies demonstrate that although the growth rates of both A. fumigatus and A. niger are sensitive to the addition of exogenous cAMP, the response of each organism is distinct and dependent on the carbon source used.

Molecular cloning of Aspergillus fumigatus CgrA, the ortholog of a conserved fungal nucleolar protein

In this report we describe the cloning of cgrA, the Aspergillus fumigatus ortholog of the yeast nucleolar protein Cgr1p. The cgrA complementary DNA (cDNA) contains a single open reading frame that would encode a protein of 114 amino acids that has 42% sequence identity to yeast Cgrlp. Heterologous expression of a green fluorescent protein (GFP)-tagged A. fumigatus cgrA gene demonstrated that the CgrA protein could localize to the yeast nucleolus. Moreover, the cgrA cDNA complemented the growth deficiency caused by inducible depletion of intracellular Cgr1p levels in yeast. These results support an orthologous relationship between the CgrA and Cgr1 proteins, and open the way for future studies into the potential value of nucleolar proteins as antifungal targets.