The core components of eisosomes, Pil1 and Lsp1, are membrane-sculpting BAR proteins. In addition, TORC2 substrates Slm1 and Slm2 have F-BAR domains that are needed for targeting into eisosomes. Results support a model in which BAR domain protein-mediated membrane bending leads to domain formation within the plasma membrane.

We identified agtA, a gene that encodes the specific dicarboxylic amino acid transporter of Aspergillus nidulans. The deletion of the gene resulted in loss of utilization of aspartate as a nitrogen source and of aspartate uptake, while not completely abolishing glutamate utilization. Kinetic constants showed that AgtA is a high-affinity dicarboxylic amino acid transporter and are in agreement with those determined for a cognate transporter activity identified previously. The gene is extremely sensitive to nitrogen metabolite repression, depends on AreA for its expression, and is seemingly independent from specific induction. We showed that the localization of AgtA in the plasma membrane necessitates the ShrA protein and that an active process elicited by ammonium results in internalization and targeting of AgtA to the vacuole, followed by degradation. Thus, nitrogen metabolite repression and ammonium-promoted vacuolar degradation act in concert to downregulate dicarboxylic amino acid transport activity.Amino acids can be utilized by saprophytic fungi as nitrogen and/or carbon sources. Their uptake is mediated by transmembrane proteins belonging to the specific fungal YAT (TC 2.A.3.10, yeast amino acid transporter) family, a member of the APC (amino acid polyamine choline) superfamily (25), which shows a wide range of substrate specificities and includes representatives in all realms of life (53). In Saccharomyces cerevisiae (51), 18 YAT transporters have been functionally characterized, while only a few have been studied in other organisms (8,25,35,57,67,68,69,72,76; Saccharomyces genome database at http://www.yeastgenome.org/). The YAT family transporters share a common predicted topology, comprising 12 transmembrane domains, and show, even among proteins with completely different substrate specificities, a high degree of sequence identity (2, 25). The transporters of the dicarboxylic amino acids glutamate and aspartate have been characterized in S. cerevisiae (DIP5; 47) and Penicillium chrysogenum (PcDIP5; 68) and are members of this family. In A. nidulans, specific dicarboxylic amino acid transport activity and certain aspects of its regulation were previously reported (24, 26, 42, 51, 52), but the corresponding gene(s) was not characterized.In fungi, the genes that encode transporters and enzyme activities involved in nitrogen source utilization are subject to tight transcriptional and/or posttranscriptional controls. Preferred nitrogen sources (such as ammonium and glutamine) repress the transcription of genes involved in the utilization of metabolically less favorable nitrogen sources such as nitrate, purines, or amino acids. In A. nidulans, nitrogen metabolite repression acts by inactivating the AreA GATA transcriptional activator (30) by a number of concurring mechanisms (36, 66). In S. cerevisiae, a transcriptional repression mechanism similar but not identical to the one described above for A. nidulans is operative (see reference 33 for a review).In addition to being subject to transcriptional regulati...

Summary Type I casein kinases are highly conserved among Eukaryotes. Of the two Aspergillus nidulans casein kinases I, CkiA is related to the δ/ε mammalian kinases and to Saccharomyces cerevisiæ Hrr25p. CkiA is essential. Three recessive ckiA mutations leading to single residue substitutions, and downregulation using a repressible promoter, result in partial loss‐of‐function, which leads to a pleiotropic defect in amino acid utilization and resistance to toxic amino acid analogues. These phenotypes correlate with miss‐routing of the YAT plasma membrane transporters AgtA (glutamate) and PrnB (proline) to the vacuole under conditions that, in the wild type, result in their delivery to the plasma membrane. Miss‐routing to the vacuole and subsequent transporter degradation results in a major deficiency in the uptake of the corresponding amino acids that underlies the inability of the mutant strains to catabolize them. Our findings may have important implications for understanding how CkiA, Hrr25p and other fungal orthologues regulate the directionality of transport at the ER‐Golgi interface.