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J Thorner

Publications and source records attributed to J Thorner.

At least 73 records · Page 4Linked to original sources
PubMed1992

Regulatory subunit (CNB1 gene product) of yeast Ca2+/calmodulin-dependent phosphoprotein phosphatases is required for adaptation to pheromone.

By using an assay specific for detection of calcineurin, a Ca2+/calmodulin-dependent phosphoprotein phosphatase, this enzyme was purified approximately 5,000-fold from extracts of the yeast Saccharomyces cerevisiae. Cna1p and Cna2p, the products of two yeast genes encoding the catalytic (A) subunits of calcineurin, were major constituents of the purified fraction. A third prominent component of apparent molecular mass 16 kDa displayed several properties, including ability to bind 45Ca2+, that are characteristic of the regulatory (B) subunit of mammalian calcineurin and was recognized by an antiserum raised against bovine calcineurin. These antibodies were used to isolate the structural gene (CNB1) encoding this protein from a yeast expression library in the vector lambda gt11. The nucleotide sequence of CNB1 predicted a polypeptide similar in length and highly related in amino acid sequence (56% identity) to the mammalian calcineurin B subunit. Like its counterpart in higher cells, yeast Cnb1p was myristoylated at its N terminus. Mutants lacking Cnb1p, or all three calcineurin subunits (Cna1p, Cna2p, and Cnb1p), were viable. Extracts of cnb1 delta mutants contained no detectable calcineurin activity, even though Cna1p and Cna2p were present at normal levels, suggesting that the B subunit is required for full enzymatic activity in vitro. As was observed previously for MATa cna1 cna2 double mutants, MATa cnb1 mutants were defective in their ability to recover from alpha-factor-induced growth arrest. Thus, the B subunit also is required for the function of calcineurin in promoting adaptation of haploid yeast cells to pheromone in vivo.

Amino Acid Sequence↗
PubMed1992

Secretion of peptides and proteins lacking hydrophobic signal sequences: the role of adenosine triphosphate-driven membrane translocators.

In this review, we will emphasize the role of ATP-dependent membrane transporters in protein export and intracellular protein trafficking in prokaryotic and eukaryotic cells. ATP-binding-cassette (ABC)-transport proteins, also termed "traffic ATPases," belong to a superfamily of ubiquitous ATP-driven membrane transporters that share extensive sequence similarity and highly conserved domain organization. They are implicated in a remarkable variety of transmembrane transport processes, including the transport of ions, heavy metals, sugars, anticancer drugs, amino acids, oligopeptides, and proteins. Bacterial ABC-proteins include the well-characterized periplasmic permeases involved in nutrient uptake, but also include protein secretion systems, such as the exporter for the Escherichia coli enterotoxin hemolysin A. Prominent eukaryotic members of this superfamily include the human P-glycoprotein (which is associated with the phenomenon of multiple drug resistance in tumor cells), the product of the cystic fibrosis gene (CFTR), the gene (pfmdr) implicated in chloroquine resistance of the malarial parasite, putative peptide transporters encoded at the locus for the class II major histocompatibility complex (MHC), and the yeast Ste6 transporter which mediates export of a peptide hormone that lacks a classical hydrophobic signal peptide. The well-established function of prokaryotic ABC-transporters in the secretion of proteins without typical signal sequences, and the example set by the Ste6 transporter, have led to the reasonable hypothesis that certain ABC-proteins in animal cells may be operating by a similar mechanism to mediate the export of a new class of secretory proteins, those lacking a classical hydrophobic signal peptide.

Adenosine Triphosphate↗
PubMed1991

Yeast has homologs (CNA1 and CNA2 gene products) of mammalian calcineurin, a calmodulin-regulated phosphoprotein phosphatase.

Calcineurin, or phosphoprotein phosphatase type 2B (PP2B), is a calmodulin-regulated phosphoprotein phosphatase. We isolated a gene encoding a yeast PP2B homolog (CNA1) by screening a yeast genomic DNA library in the expression vector lambda gt11, first with 125I-labeled yeast calmodulin and then with a human cDNA encoding the catalytic (or A) subunit of calcineurin. The predicted CNA1 gene product is 54% identical to its mammalian counterpart. Using the polymerase chain reaction (PCR) with oligonucleotide primers based on sequences conserved between CNA1 and mammalian PP2B genes, we isolated a second gene, CNA2. CNA2 is identical to PP2Bw, a partial cDNA clone previously described by others as originating from rabbit brain tissue. Our findings demonstrate that a unicellular eukaryote contains phosphoprotein phosphatases of the 2B class. Haploid cells containing a single cna1 or cna2 null mutation, or both mutations, were viable. MATa cna1 cna2 double mutants were more sensitive than wild-type cells or either single mutant to growth arrest induced by the mating pheromone alpha factor and failed to resume growth during continuous exposure to alpha factor. Thus, calcineurin action antagonizes the mating-pheromone response pathway.

Amino Acid Sequence↗
PubMed1991

Multiple Ca2+/calmodulin-dependent protein kinase genes in a unicellular eukaryote.

We purified a Ca2+/calmodulin (CaM)-dependent protein kinase (CaM kinase) from the yeast Saccharomyces cerevisiae with properties similar to mammalian type II CaM kinases. Degenerate oligonucleotides designed on the basis of the amino acid sequence of tryptic peptides from the 55 kd subunit of the yeast CaM kinase were used to isolate its gene from a set of lambda gt11-yeast genomic DNA phage clones initially selected by the ability to bind 125I-labelled yeast CaM. The cloned gene (CMK1) encodes an open reading frame that is homologous to the sequences of vertebrate type II CaM kinases. Several criteria demonstrated that the CMK1 gene product is the 55 kd polypeptide. Neither over-production (11-fold) nor complete elimination of the CMK1 gene product had any detectably deleterious effect on yeast cell growth. Extracts from cmk1 delta cells, which lacked detectable p55 using an antiserum raised against a Staphylococcus aureus protein A-CMK1 fusion protein, possessed significant residual Ca2+/CAM-dependent protein kinase activity. Using the CMK1 gene as a probe at low stringency, a second gene (CMK2) encoding another CaM-dependent protein kinase with striking sequence similarity to CMK1 was cloned. Deletion of CMK2, or both CMK1 and CMK2, was not lethal, although loss of CMK2 caused a slow rate of spore germination.

Amino Acid Sequence↗
PubMed1990

Saccharomyces cerevisiae STE14 gene is required for COOH-terminal methylation of a-factor mating pheromone.

Saccharomyces cerevisiae a-factor is a dodecapeptide pheromone in which the carboxyl group of the COOH-terminal cysteine residue is methyl-esterified and the sulfhydryl side chain is conjugated in thioether linkage to a farnesyl moiety. We found that MAT a ste14 mutant cells secreted a biologically inactive form of a-factor which had more hydrophilic character than the wild-type pheromone. The authentic pheromone could be metabolically labeled with [methyl-3H]methionine, and the resulting COOH-terminal methyl ester could be removed by mild alkaline hydrolysis. In contrast, a-factor secreted by ste14 mutants did not incorporate a base-labile 3H-methyl moiety. Base treatment converted the normal pheromone into a form which was biologically inactive and which comigrated with the ste14 form of the peptide upon thin-layer chromatography. These results indicate that STE14 gene function is required for COOH-terminal methylation of a-factor.

DNA Transposable Elements↗
PubMed1990

Control of yeast mating signal transduction by a mammalian beta 2-adrenergic receptor and Gs alpha subunit.

To facilitate functional and mechanistic studies of receptor-G protein interactions, [corrected] the human beta 2-adrenergic receptor (h beta-AR) has been expressed in Saccharomyces cerevisiae. This was achieved by placing a modified h beta-AR gene under control of the galactose-inducible GAL1 promoter. After induction by galactose, functional h beta-AR was expressed at a concentration several hundred times as great as that found in any human tissue. As determined from competitive ligand binding experiments, h beta-AR expressed in yeast displayed characteristic affinities, specificity, and stereoselectivity. Partial activation of the yeast pheromone response pathway by beta-adrenergic receptor agonists was achieved in cells coexpressing h beta-AR and a mammalian G protein (Gs) alpha subunit-demonstrating that these components can couple to each other and to downstream effectors when expressed in yeast. This in vivo reconstitution system provides a new approach for examining ligand binding and G protein coupling to cell surface receptors.

Amino Acid Sequence↗
PubMed1990

A candidate protein kinase C gene, PKC1, is required for the S. cerevisiae cell cycle.

Probes derived from cDNAs encoding isozymes of rat protein kinase C (PKC) were used to screen the genome of the budding yeast S. cerevisiae. A single gene (PKC1) was isolated that encodes a putative protein kinase closely related to the alpha, beta, and gamma subspecies of mammalian PKC. Deletion of PKC1 resulted in recessive lethality. Cells depleted of the PKC1 gene product displayed a uniform phenotype, a characteristic of cell division cycle (cdc) mutants, and arrested cell division at a point subsequent to DNA replication, but prior to mitosis. Unlike most cdc mutants, which continue to grow in the absence of cell division, PKC1-depleted cells arrested growth with small buds. PKC1 may regulate a previously unrecognized checkpoint in the cell cycle.

Amino Acid Sequence↗
PubMed1990

Beta and gamma subunits of a yeast guanine nucleotide-binding protein are not essential for membrane association of the alpha subunit but are required for receptor coupling.

Conditions were devised to demonstrate GTP-regulated coupling between the yeast STE2-encoded receptor and its cognate guanine nucleotide-binding protein (G protein). Treatment of partially purified membranes with guanosine 5'-[gamma-thio]triphosphate (GTP[gamma-S]) converted the receptor from a high-affinity state (Kd = 17 nM) to a much lower affinity state (Kd approximately 150 nM), as judged by three independent criteria: rate of ligand (alpha-factor) dissociation, equilibrium binding, and antagonist competition. Expression of STE2 from the GAL1 promoter in MATa/MAT alpha diploids, which do not express GPA1 (encoding G protein alpha subunit, G alpha), STE4 (encoding G protein beta subunit, G beta), and STE18 (encoding G protein gamma subunit, G gamma) but do express another G protein alpha subunit (product of GPA2), yielded a single class of low-affinity receptors that were GTP[gamma-S]-insensitive, indicating that STE2 gene product cannot couple productively with other G proteins, even in the absence of competition by its cognate G protein. By using gpa1, STE4, and ste18 mutations, it was found that all three G protein subunits were required for functional coupling, as judged by the absence of high-affinity receptors when any of the three gene products was altered. This finding demonstrates that G beta and G gamma subunits are essential for formation of a productive complex between a G alpha subunit and its corresponding receptor. Wild-type STE4 and STE18 gene products were not essential for membrane localization of the GPA1 gene product, as indicated by cell fractionation and immunological analyses, suggesting that G beta and G gamma subunits interact with the receptor or make the G alpha subunit competent to associate correctly with the receptor, or both.

Cell Membrane↗
PubMed1990

Human fur gene encodes a yeast KEX2-like endoprotease that cleaves pro-beta-NGF in vivo.

Extracts from BSC-40 cells infected with vaccinia recombinants expressing either the yeast KEX2 prohormone endoprotease or a human structural homologue (fur gene product) contained an elevated level of a membrane-associated endoproteolytic activity that could cleave at pairs of basic amino acids (-LysArg- and -ArgArg-). The fur-directed activity (furin) shared many properties with Kex2p including activity at pH 7.3 and a requirement for calcium. By using antifurin antibodies, immunoblot analysis detected two furin translation products (90 and 96 kD), while immunofluorescence indicated localization to the Golgi apparatus. Coexpression of either Kex2p or furin with the mouse beta-nerve growth factor precursor (pro-beta-NGF) resulted in greatly enhanced conversion of the precursor to mature nerve growth factor. Thus, the sequence homology shared by furin and the yeast KEX2 prohormone processing enzyme is reflected by significant functional homology both in vitro and in vivo.

Amino Acid Sequence↗
PubMed1990

Novel yeast protein kinase (YPK1 gene product) is a 40-kilodalton phosphotyrosyl protein associated with protein-tyrosine kinase activity.

Extracts of bakers' yeast (Saccharomyces cerevisiae) contain protein-tyrosine kinase activity that can be detected with a synthetic Glu-Tyr copolymer as substrate (G. Schieven, J. Thorner, and G.S. Martin, Science 231:390-393, 1986). By using this assay in conjunction with ion-exchange and affinity chromatography, a soluble tyrosine kinase activity was purified over 8,000-fold from yeast extracts. The purified activity did not utilize typical substrates for mammalian protein-tyrosine kinases (enolase, casein, and histones). The level of tyrosine kinase activity at all steps of each preparation correlated with the content of a 40-kDa protein (p40). Upon incubation of the most highly purified fractions with Mn-ATP or Mg-ATP, p40 was the only protein phosphorylated on tyrosine. Immunoblotting of purified p40 or total yeast extracts with antiphosphotyrosine antibodies and phosphoamino acid analysis of 32P-labeled yeast proteins fractionated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicated that the 40-kDa protein is normally phosphorylated at tyrosine in vivo. 32P-labeled p40 immunoprecipitated from extracts of metabolically labeled cells by affinity-purified anti-p40 antibodies contained both phosphoserine and phosphotyrosine. The gene encoding p40 (YPK1) was cloned from a yeast genomic library by using oligonucleotide probes designed on the basis of the sequence of purified peptides. As deduced from the nucleotide sequence of YPK1, p40 is homologous to known protein kinases, with features that resemble known protein-serine kinases more than known protein-tyrosine kinases. Thus, p40 is a protein kinase which is phosphorylated in vivo and in vitro at both tyrosine and serine residues; it may be a novel type of autophosphorylating tyrosine kinase, a bifunctional (serine/tyrosine-specific) protein kinase, or a serine kinase that is a substrate for an associated tyrosine kinase.

Amino Acid Sequence↗
PubMed1989

Saccharomyces cerevisiae STE6 gene product: a novel pathway for protein export in eukaryotic cells.

Saccharomyces cerevisiae MATa cells release a lipopeptide mating pheromone, a-factor. Radiolabeling and immunoprecipitation show that MATa ste6 mutants produce pro-a-factor and mature a-factor intracellularly, but little or no extracellular pheromone. Normal MATa cells carrying a multicopy plasmid containing both MFa1 (pro-a-factor structural gene) and the STE6 gene secrete a-factor at least five times faster than the same cells carrying only MFa1 in the same vector. The nucleotide sequence of the STE6 gene predicts a 1290 residue polypeptide with multiple membrane spanning segments and two hydrophilic domains, each strikingly homologous to a set of well-characterized prokaryotic permeases (including hlyB, oppD, hisP, malK and pstB) and sharing even greater identity with mammalian mdr (multiple drug resistance) transporters. These results suggest that the STE6 protein in yeast, and possibly mdr in animals, is a transmembrane translocator that exports polypeptides by a route independent of the classical secretory pathway.

ATP-Binding Cassette Transporters↗
PubMed1989

Functional expression of the yeast alpha-factor receptor in Xenopus oocytes.

The STE2 gene of the yeast Saccharomyces cerevisiae encodes a 431-residue polypeptide that has been shown by chemical cross-linking and genetic studies to be a component of the receptor for the peptide mating pheromone, alpha-factor. To demonstrate directly that the ligand binding site of the alpha-factor receptor is comprised solely of the STE2 gene product, the STE2 protein was expressed in Xenopus oocytes. Oocytes microinjected with synthetic STE2 mRNA displayed specific surface binding for 35S-labeled alpha-factor (up to 40 sites/micron2/ng RNA). Oocytes injected with either STE2 antisense RNA or heterologous receptor mRNA (nicotinic acetylcholine receptor alpha, beta, gamma, and delta subunit mRNAs) showed no binding activity (indistinguishable from uninjected control oocytes). The apparent KD (7 nM) of the alpha-factor binding sites expressed on the oocyte surface, determined by competition binding studies, agreed with the values reported for intact yeast cells and yeast plasma membrane fractions. These findings demonstrate that the STE2 gene product is the only yeast polypeptide required for biogenesis of a functional alpha-factor receptor. Electrophysiological measurements indicated that the membrane conductance of oocytes injected with STE2 mRNA, or with both STE2 and GPA1 (encoding a yeast G protein alpha-subunit) mRNAs, did not change and was not affected by pheromone binding. Thus, the alpha-factor receptor, like mammalian G protein-coupled receptors, apparently lacks activity as an intrinsic or ligand-gated ion channel. This report is the first instance in which a membrane-bound receptor from a unicellular eukaryote has been expressed in a vertebrate cell.

Animals↗
PubMed1989

Intracellular targeting and structural conservation of a prohormone-processing endoprotease.

The prohormone-processing endoprotease (KEX2 gene product) of the yeast Saccharomyces cerevisiae is a membrane-bound, 135,000-dalton glycoprotein, which contains both asparagine-linked and serine- and threonine-linked oligosaccharide and resides in a secretory compartment. Analysis of mutant kex2 genes truncated at their 3' end indicates that carboxyl terminal domains of the enzyme are required for its proper localization within the cell. A human gene product, "furin," shares 50% identity with the catalytic domain of Kex2 protease and is, therefore, a candidate for a human prohormone-processing enzyme.

Amino Acid Sequence↗
PubMed1989

A putative protein kinase overcomes pheromone-induced arrest of cell cycling in S. cerevisiae.

MATa cells carrying an sst2 mutation are unable to recover from the G1-specific cell cycle arrest induced by the mating pheromone alpha factor. The KSS1 gene, when overexpressed, suppresses this adaptation defect. KSS1 overexpression also suppresses the recovery defect manifested by cells expressing an alpha factor receptor lacking its 136 amino acid cytoplasmic tail. Because SST2 product and the receptor tail contribute independently to events that allow recovery from pheromone-induced growth arrest, KSS1 function defines a third independent process that promotes desensitization. The KSS1 gene encodes an apparent protein kinase homologous to the CDC28 (S. cerevisiae) and cdc2+ (S. pombe) gene products. The recovery-promoting activity of the KSS1 gene requires a functional WHI1 gene, which encodes a yeast homolog to animal cyclins, suggesting that the KSS1 and WHI1 proteins act in the same growth control pathway.

Amino Acid Sequence↗