51 research outputs found
Evolutionarily assembled cis-regulatory module at a human ciliopathy locus.
No full textNeighboring genes are often coordinately expressed within cis-regulatory modules, but evidence that nonparalogous genes share functions in mammals is lacking. Here, we report that mutation of either TMEM138 or TMEM216 causes a phenotypically indistinguishable human ciliopathy, Joubert syndrome. Despite a lack of sequence homology, the genes are aligned in a head-to-tail configuration and joined by chromosomal rearrangement at the amphibian-to-reptile evolutionary transition. Expression of the two genes is mediated by a conserved regulatory element in the noncoding intergenic region. Coordinated expression is important for their interdependent cellular role in vesicular transport to primary cilia. Hence, during vertebrate evolution of genes involved in ciliogenesis, nonparalogous genes were arranged to a functional gene cluster with shared regulatory elements
Identification of yeast component A: reconstitution of the geranylgeranyltransferase that modifies Ypt1p and Sec4p.
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Characterization of new mutants in the early part of the yeast secretory pathway isolated by a [3H]mannose suicide selection.
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No full textEndoplasmic Reticulum (ER)-derived COPII coated vesicles constitutively transport secretory cargo to the Golgi. However, during starvation-induced stress, COPII vesicles have been implicated as a membrane source for autophagosomes, distinct organelles that engulf cellular components for degradation by macroautophagy (hereafter called autophagy). How cells regulate core trafficking machinery to fulfill dramatically different cellular roles in response to environmental cues is unknown. Here we show that phosphorylation of conserved amino acids on the membrane-distal surface of the Saccharomyces cerevisiae COPII cargo adaptor, Sec24, reprograms COPII vesicles for autophagy. We also show casein kinase 1 (Hrr25) is a key kinase that phosphorylates this regulatory surface. During autophagy, Sec24 phosphorylation regulates autophagosome number and its interaction with the C-terminus of Atg9, a component of the autophagy machinery required for autophagosome initiation. We propose that the acute need to produce autophagosomes during starvation drives the interaction of Sec24 with Atg9 to increase autophagosome abundance
Osmohomeostasis and vacuole biogenesis genes in the yeast saccharomyces cerevisiae
No full textThe putative role of the S. cerevisiae vacuole in osmohomeostasis, as well as its biogenesis was analysed by taking a mutational approach. 97 mutants unable to tolerate high concentrations of salt were isolated and examined for aberrant vacuolar phenotypes. A comprehensive phenotypic analysis was able to demonstrate that apart from osmosensitivity most mutations conferred other properties such as altered vacuolar morphology, the inability to perform gluconeogenesis and/or the mislocalization of vacuolar proteins to the cell surface. The mutants fall into at least 20 complementation groups, termed ssv for salt sensitive vacuolar mutants, of which 3 genetically overlap with complementation groups isolated by others. This analysis provides evidence that in 5. cerevisiae correct vacuolar biogenesis is required for osmotolerance as well as other important cellular processes. To elucidate vacuolar osmohomeostasis at the molecular level, one gene, SSV7, was cloned from a genomic DNA library by complementation of a ssv7-l mutation and its sequence determined. It encodes a novel 927 amino acid protein with limited structural homology to the functional domains of two nucleotide exchange factors from 5. cerevisiae, namely CDC25 and BUD5. A mutation in the SSV7 gene confers a pleiotropic phenotype including fragmented vacuoles and the absence of a nucleus. The mutation apparently uncouples mitosis from cell growth, which results in an increased cell size of a ssv7-l mutant. The role of SSV7 in the general concept of vacuole biogenesis is discussed, as is the observed fact that a number of mutants in intermediate biosynthetic pathways confer a vacuolar protein sorting defect
Septin-dependent compartmentalization of the endoplasmic reticulum during yeast polarized growth
No full textPolarized cells frequently use diffusion barriers to separate plasma membrane domains. It is unknown whether diffusion barriers also compartmentalize intracellular organelles. We used photobleaching techniques to characterize protein diffusion in the yeast endoplasmic reticulum (ER). Although a soluble protein diffused rapidly throughout the ER lumen, diffusion of ER membrane proteins was restricted at the bud neck. Ultrastructural studies and fluorescence microscopy revealed the presence of a ring of smooth ER at the bud neck. This ER domain and the restriction of diffusion for ER membrane proteins through the bud neck depended on septin function. The membrane-associated protein Bud6 localized to the bud neck in a septin-dependent manner and was required to restrict the diffusion of ER membrane proteins. Our results indicate that Bud6 acts downstream of septins to assemble a fence in the ER membrane at the bud neck. Thus, in polarized yeast cells, diffusion barriers compartmentalize the ER and the plasma membrane along parallel lines
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