Bioactive small molecules are critical in Aspergillus species during their development and interaction with other organisms. Genes dedicated to their production are encoded in clusters that can be located throughout the genome. We show that deletion of hdaA, encoding an Aspergillus nidulans histone deacetylase (HDAC), causes transcriptional activation of two telomere-proximal gene clusters-and subsequent increased levels of the corresponding molecules (toxin and antibiotic)-but not of a telomere-distal cluster. Introduction of two additional HDAC mutant alleles in a ⌬hdaA background had minimal effects on expression of the two HdaA-regulated clusters. Treatment of other fungal genera with HDAC inhibitors resulted in overproduction of several metabolites, suggesting a conserved mechanism of HDAC repression of some secondary-metabolite gene clusters. Chromatin regulation of small-molecule gene clusters may enable filamentous fungi to successfully exploit environmental resources by modifying chemical diversity.A distinguishing characteristic of filamentous fungi is their ability to produce a wide variety of small molecules that aid in their survival and pathogenicity. These include compounds, such as pigments, that play a role in virulence and protect the fungus from environmental damage, as well as toxins that kill host tissues or hinder competition from other organisms. These secondary metabolites (SM) (27) can also impact humans in both beneficial and detrimental ways. Many widely used pharmaceuticals are natural products of fungi, as are some of the most potent carcinogens yet identified. Genetic studies, augmented by analysis of whole genome sequences, have revealed that most fungal SM biosynthetic genes are found in compact clusters functioning as individual genetic loci (27). The genus Aspergillus, whose members include toxinproducing pathogens (Aspergillus flavus and A. fumigatus) and pharmaceutical-producing species (A. nidulans and A. terreus), is renowned for prodigious metabolite production and serves as the model for natural-product exploration. Detailed comparison of the genomes of several aspergilli indicates a genomic landscape in which the greatest diversity between species is represented in these SM clusters (28).There has been considerable debate as to the role that gene clustering plays in the secondary metabolism of fungi. Such gene arrangement must be advantageous to the fungus; if natural selection did not favor clustering, one would assume that processes such as gene translocation and unequal crossing over would have caused dispersal over evolutionary history. Support for horizontal transfer from prokaryotes, in which genes are often arranged into operons, exists for the penicillin biosynthetic cluster (9) but not for other fungal clusters. A prokaryotic gene transfer hypothesis is weakened by the fact that fungal SM genes often contain introns and employ codon usage typical of other fungal genes. Another hypothesis holds that clustering provides a selective advantage to the cluster itself i...

The readout of the genetic information of eukaryotic organisms is significantly regulated by modifications of DNA and chromatin proteins. Chromatin alterations induce genome-wide and local changes in gene expression and affect a variety of processes in response to internal and external signals during growth, differentiation, development, in metabolic processes, diseases, and abiotic and biotic stresses. This review aims at summarizing the roles of histone H1 and the acetylation and methylation of histones in filamentous fungi and links this knowledge to the huge body of data from other systems. Filamentous fungi show a wide range of morphologies and have developed a complex network of genes that enables them to use a great variety of substrates. This fact, together with the possibility of simple and quick genetic manipulation, highlights these organisms as model systems for the investigation of gene regulation. However, little is still known about regulation at the chromatin level in filamentous fungi. Understanding the role of chromatin in transcriptional regulation would be of utmost importance with respect to the impact of filamentous fungi in human diseases and agriculture. The synthesis of compounds (antibiotics, immunosuppressants, toxins, and compounds with adverse effects) is also likely to be regulated at the chromatin level.

Acetylation is the most prominent modification on core histones that strongly affects nuclear processes such as DNA replication, DNA repair and transcription. Enzymes responsible for the dynamic equilibrium of histone acetylation are histone acetyltransferases (HATs) and histone deacetylases (HDACs). In this paper we describe the identification of novel HDACs from the filamentous fungi Aspergillus nidulans and the maize pathogen Cochliobolus carbonum. Two of the enzymes are homologs of Saccharomyces cerevisiae HOS3, an enzyme that has not been identified outside of the established yeast systems until now. One of these homologs, HosB, showed intrinsic HDAC activity and remarkable resistance against HDAC inhibitors like trichostatin A (TSA) when recombinant expressed in an Escherichia coli host system. Phylo genetic analysis revealed that HosB, together with other fungal HOS3 orthologs, is a member of a separate group within the classical HDACs. Immunological investigations with partially purified HDAC activities of Aspergillus showed that all classical enzymes are part of high molecular weight complexes and that a TSA sensitive class 2 HDAC constitutes the major part of total HDAC activity of the fungus. However, further biochemical analysis also revealed an NAD(+)-dependent activity that could be separated from the other activities by different types of chromatography and obviously represents an enzyme of the sirtuin class.

A C-terminal motif of an A. nidulans class 1 histone deacetylase (HDAC) is required for catalytic activity and viability of the fungus. Moreover, this motif seems to play a decisive role for growth and development of other fungal species. Thus, this enzyme/motif may represent a promising target for HDAC-inhibitors acting as antifungal agents.

Histone deacetylases (HDACs) catalyze the removal of acetyl groups from the -amino group of distinct lysine residues in the amino-terminal tail of core histones. Since the acetylation status of core histones plays a crucial role in fundamental processes in eukaryotic organisms, such as replication and regulation of transcription, recent research has focused on the enzymes responsible for the acetylation/deacetylation of core histones. Very recently, we showed that HdaA, a member of the Saccharomyces cerevisiae HDA1-type histone deacetylases, is a substantial contributor to total HDAC activity in the filamentous fungus Aspergillus nidulans. Now we demonstrate that deletion of the hdaA gene indeed results in the loss of the main activity peak and in a dramatic reduction of total HDAC activity. In contrast to its orthologs in yeast and higher eukaryotes, HdaA has strong intrinsic activity as a protein monomer when expressed as a recombinant protein in a prokaryotic expression system. In vivo, HdaA is involved in the regulation of enzymes which are of vital importance for the cellular antioxidant response in A. nidulans. Consequently, ⌬hdaA strains exhibit significantly reduced growth on substrates whose catabolism generates molecules responsible for oxidative stress conditions in the fungus. Our analysis revealed that reduced expression of the fungal catalase CatB is jointly responsible for the significant growth reduction of the hdaA mutant strains.In eukaryotic organisms, DNA and highly basic nuclear proteins, the histones, constitute the nucleosome, which is the essential structural subunit of the chromatin. The fact that the N-terminal extensions of the core histones contain distinct sites for various posttranslational modifications alters our view of chromatin as being a static entity for the efficient packing of the genomic DNA into the nucleus of the cell. Today it is accepted that, in addition to its structural role, chromatin has an important regulatory function during DNA replication and repair, cell cycle control, cell aging, and transcription (for a review, see reference 59).Antagonistic enzymes such as kinases/phosphatases (10, 39), histone methyltransferases/demethylases (for a review, see reference 9), and histone acetyltransferases/deacetylases (for a review, see reference 38) are responsible for a dynamic equilibrium of chromatin regulating modifications of the histone tails.The acetylation of distinct lysine residues of H2A, H2B, H3, and H4 is the most prominent dynamic histone modification allowing or denying the access of numerous regulatory proteins, such as transcription factors, to distinct regions of genomic DNA. Although histone acetylation is by far the beststudied type of histone modification, our understanding of how this modification is linked to processes such as the regulation of transcription is still very limited. However, acetylated histones are a characteristic feature of transcriptionally active chromatin (2), and hypoacetylated histones accumulate within transcriptionally silenc...