Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.2.1.26 (invertase)
 4,927 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Clathrin-coated membranes are intimately associated with a variety of protein transport processes in eukaryotic cells, yet no direct test of clathrin function has been possible. The data presented demonstrate that Saccharomyces cerevisiae does not require clathrin for either cell growth or protein secretion. Antiserum to the yeast clathrin heavy chain has been used to isolate a molecular clone of the heavy chain gene (CHC1) from a library of yeast DNA in lambda gt11. Clathrin-deficient mutant yeast have been obtained by replacing the single chromosomal CHC1 gene with a disrupted version of the cloned DNA. Cells harboring a nonfunctional chc1 allele produce no immunoreactive heavy chain polypeptide, and vesicles prepared from mutant cells are devoid of clathrin heavy and light chains. Although clathrin-deficient cells grow two to three times more slowly than normal, secretion of invertase occurs at a nearly normal rate. Therefore protein transport through the secretory pathway is not obligately coupled to the formation of clathrin-coated vesicles.
 ...
PMID:A test of clathrin function in protein secretion and cell growth. 286 11

Clathrin is important but not essential for yeast cell growth and protein secretion. Diploid Saccharomyces cerevisiae cells heterozygous for a clathrin heavy-chain gene (CHC1) disruption give rise to viable, slow-growing, clathrin heavy-chain-deficient meiotic progeny (G. Payne and R. Schekman, Science 230:1009-1014, 1985). The possibility that extragenic suppressors account for growth of clathrin-deficient cells was examined by deletion of CHC1 from haploid cell genomes by single-step gene transplacement and independently by introduction of a centromere plasmid carrying the complete CHC1 gene into diploid cells before eviction of a chromosomal CHC1 locus and subsequent tetrad analysis. Both approaches yielded clathrin-deficient haploid strains. In mutants missing at least 95% of the CHC1 coding domain, transcripts related to CHC1 were not detected. The time course of invertase modification and secretion was measured to assess secretory pathway functions in the viable clathrin-deficient cells. Core-glycosylated invertase was converted to the mature, highly glycosylated form at equivalent rates in mutant and wild-type cells. Export of mature invertase from mutant cells was delayed but not prevented. Abnormal vacuoles, accumulated vesicles, and Golgi body-derived structures were visualized in mutant cells by electron microscopy. We conclude that extragenic suppressors do not account for the viability of clathrin-deficient cells and, furthermore, that many standard laboratory strains can sustain a CHC1 disruption. Clathrin does not appear to mediate protein transfer from the endoplasmic reticulum to the Golgi body but may function at a later stage of the secretory pathway.
 ...
PMID:Genetic and biochemical characterization of clathrin-deficient Saccharomyces cerevisiae. 332 82

Clathrin and its associated proteins constitute a major class of coat proteins involved in vesicle budding during membrane transport. An interesting characteristic of the yeast clathrin heavy chain gene (CHC1) is that in some strains a CHC1 deletion is lethal, while in others it is not. Recently, our laboratory developed a screen that identified five multicopy suppressors that can rescue lethal strains of clathrin heavy chain-deficient yeast (Chc - scd1-i) to viability. One of these suppressors, SCD5, encodes a novel protein of 872 amino acids containing two regions of repeated motifs of unknown function. Deletion of SCD5 has shown that it is essential for cell growth at 30 degrees C. scd5-delta strains carrying low copy plasmids encoding C-terminal truncations of Scd5p are temperature sensitive for growth at 37 degrees C. At the nonpermissive temperature, cells expressing a 338-amino acid deletion (Scd5P-delta 338) accumulate an internal pool of fully glycosylated invertase and mature alpha-factor, while processing and sorting of the vacuolar hydrolase carboxypeptidase Y is normal. The truncation mutant also accumulates 80- to 100-nm vesicles similar to many late sec mutants. Moreover, at 34 degrees C, overexpression of Scd5p suppresses the temperature sensitivity of a sec2 mutant, which is blocked at a post-Golgi step of the secretory pathway. Biochemical analyses indicate that approximately 50% of Scd5p sediments with a 100,000 x g membrane fraction and is associated as a peripheral membrane protein. Overall, these results indicate that Scd5p is involved in vesicular transport at a late stage of the secretory pathway. Furthermore, this suggests that the lethality of clathrin-deficient yeast can be rescued by modulation of vesicular transport at this late secretory step.
 ...
PMID:SCD5, a suppressor of clathrin deficiency, encodes a novel protein with a late secretory function in yeast. 868 56

ADP-ribosylation factor (ARF) is a small GTP-binding protein that is thought to regulate the assembly of coat proteins on transport vesicles. To identify factors that functionally interact with ARF, we have performed a genetic screen in Saccharomyces cerevisiae for mutations that exhibit synthetic lethality with an arf1Delta allele and defined seven genes by complementation tests (SWA1-7 for synthetically lethal with arf1Delta). Most of the swa mutants exhibit phenotypes comparable to arf1Delta mutants such as temperature-conditional growth, hypersensitivity to fluoride ions, and partial protein transport and glycosylation defects. Here, we report that swa5-1 is a new temperature-sensitive allele of the clathrin heavy chain gene (chc1-5), which carries a frameshift mutation near the 3' end of the CHC1 open reading frame. This genetic interaction between arf1 and chc1 provides in vivo evidence for a role for ARF in clathrin coat assembly. Surprisingly, strains harboring chc1-5 exhibited a significant defect in transport of carboxypeptidase Y or carboxypeptidase S to the vacuole that was not observed in other chc1 ts mutants. The kinetics of invertase secretion or transport of alkaline phosphatase to the vacuole were not significantly affected in the chc1-5 mutant, further implicating clathrin specifically in the Golgi to vacuole transport pathway for carboxypeptidase Y.
 ...
PMID:An arf1Delta synthetic lethal screen identifies a new clathrin heavy chain conditional allele that perturbs vacuolar protein transport in Saccharomyces cerevisiae. 975 91