A genome-scale genetic interaction map was constructed by examining 5.4 million gene-gene pairs for synthetic genetic interactions, generating quantitative genetic interaction profiles for ~75% of all genes in the budding yeast, Saccharomyces cerevisiae. A network based on genetic interaction profiles reveals a functional map of the cell in which genes of similar biological processes cluster together in coherent subsets, and highly correlated profiles delineate specific pathways to define gene function. The global network identifies functional cross-connections between all bioprocesses, mapping a cellular wiring diagram of pleiotropy. Genetic interaction degree correlated with a number of different gene attributes, which may be informative about genetic network hubs in other organisms. We also demonstrate that extensive and unbiased mapping of the genetic landscape provides a key for interpretation of chemical-genetic interactions and drug target identification.

The mTOR Complex 1 (mTORC1) pathway promotes cell growth in response to many cues, including amino acids, which act through the Rag GTPases to promote mTORC1 translocation to the lysosomal surface, its site of activation. Although progress has been made in identifying positive regulators of the Rags, it is unknown if negative factors also exist. Here, we identify GATOR as a complex that interacts with the Rags and is composed of two subcomplexes we call GATOR1 and 2. Inhibition of GATOR1 subunits (DEPDC5, Nprl2, and Nprl3) makes mTORC1 signaling resistant to amino acid deprivation. In contrast, inhibition of GATOR2 subunits (Mios, WDR24, WDR59, Seh1L, Sec13) suppresses mTORC1 signaling and epistasis analysis shows that GATOR2 negatively regulates DEPDC5. GATOR1 has GTPase activating protein (GAP) activity for RagA and RagB and its components are mutated in human cancer. In cancer cells with inactivating mutations in GATOR1, mTORC1 is hyperactive and insensitive to amino acid starvation and such cells are hypersensitive to rapamycin, an mTORC1 inhibitor. Thus, we identify a key negative regulator of the Rag GTPases and reveal that, like other mTORC1 regulators, Rag function can be deregulated in cancer.

Genome-wide characterization of the in vivo cellular response to perturbation is fundamental to understanding how cells survive stress. Identifying the proteins and pathways perturbed by small molecules affects biology and medicine by revealing the mechanisms of drug action. We used a yeast chemogenomics platform that quantifies the requirement for each gene for resistance to a compound in vivo to profile 3250 small molecules in a systematic and unbiased manner. We identified 317 compounds that specifically perturb the function of 121 genes and characterized the mechanism of specific compounds. Global analysis revealed that the cellular response to small molecules is limited and described by a network of 45 major chemogenomic signatures. Our results provide a resource for the discovery of functional interactions among genes, chemicals, and biological processes.

The unfolded protein response (UPR) is an intracellular signaling pathway that relays signals from the lumen of the ER to activate target genes in the nucleus. We devised a genetic screen in the yeast Saccharomyces cerevisiae to isolate mutants that are dependent on activation of the pathway for viability. Using this strategy, we isolated mutants affecting various aspects of ER function, including protein translocation, folding, glycosylation, glycosylphosphatidylinositol modification, and ER-associated protein degradation (ERAD). Extending results gleaned from the genetic studies, we demonstrate that the UPR regulates trafficking of proteins at the translocon to balance the needs of biosynthesis and ERAD. The approach also revealed connections of the UPR to other regulatory pathways. In particular, we identified SON1/RPN4, a recently described transcriptional regulator for genes encoding subunits of the proteasome. Our genetic strategy, therefore, offers a powerful means to provide insight into the physiology of the UPR and to identify novel genes with roles in many aspects of secretory and membrane protein biogenesis.

Nuclear pore complexes (NPCs) facilitate nucleocytoplasmic transport. These massive assemblies comprise an eight-fold symmetric scaffold of architectural proteins and central-channel phenylalanine-glycine-repeat proteins forming the transport barrier. We determined the Nup85•Seh1 structure, a module in the heptameric Nup84 complex. Structural, biochemical, and genetic analyses position the Nup84 complex in two peripheral NPC rings. We establish a conserved tripartite element, the ancestral coatomer element ACE1, that reoccurs in several nucleoporins and vesicle coat proteins, providing structural evidence of coevolution from a common ancestor. We identify interactions that define the organization of the Nup84 complex based on comparison with vesicle coats and confirmed the sites by mutagenesis. We propose the NPC scaffold, like vesicle coats, is composed of polygons with vertices and edges forming a membrane-proximal lattice providing docking sites for additional nucleoporins.Exchange of macromolecules across the nuclear envelope is exclusively mediated by NPCs (1-3). Whereas much progress has been made understanding the soluble factors mediating nucleocytoplasmic transport, the structure of the ~40-60 MDa NPC itself is still largely enigmatic. Cryo-electrontomography (cryo-ET) and cryo-electronmicroscopy (cryo-EM) have established the NPC structure at low resolution (4-6). Crystal structures of scaffold NPC components are emerging (7-10), but the resolution gap still precludes fitting into the cryo-ET structure. Overall, the NPC has eight-fold rotational symmetry with an outer diameter of ~100 nm and a core scaffold ring ~30 nm wide. The central FG-repeat containing transport channel measures ~40 nm in diameter, defining the maximum size of substrates (11).The modularity of the NPC assembly suggests a path toward a high-resolution structure (12). Of the ~30 bona fide nucleoporins (Nups) that comprise the NPC, only a core subset is stably attached (13). In S. cerevisiae, this core includes two essential complexes; the heptameric Nup84 complex and the heteromeric Nic96-containing complex (hereafter called the Nic96 complex; unless noted all proteins are from S. cerevisiae). The Nup84 complex is composed of one copy each of Nup84, Nup85, Nup120, Nup133, Nup145C, Sec13 and Seh1. It self-assembles from recombinant proteins in vitro and forms a branched Y-shaped structure (14). Deletion or depletion of individual components of the Nup84 complex leads to severe assembly defects in many organisms (15)(16)(17).