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J J Jacoby

Publications and source records attributed to J J Jacoby.

11 recordsLinked to original sources
PubMed2001

The PH domain of the yeast GEF Rom2p serves an essential function in vivo.

In a screen designed to identify new upstream components of the Pkc1p-MAP kinase signal transduction pathway that responds to cell wall damage in yeast, we identified a new mutant allele of the ROM2 gene, which encodes a GDP/GTP exchange factor that acts on Rho1p. This allele, originally termed ubk1 (upstream of Bck1p) encodes a truncated protein that lacks the putative PH domain. Complementation experiments showed that genes coding for several known components of the pathway are able to suppress the ubk1 mutation to various degrees when introduced on low- or high-copy-number vectors. Analysis of several rom2 mutants showed that mutants in which the PH domain is deleted result in a phenotype indistinguishable from that of a strain deleted for the entire gene, indicating that this domain fulfills an essential function in vivo. Furthermore, we found that the growth phenotype of rom2 mutants is highly dependent on the strain background. Surprisingly, analysis of the phosphorylation status of Mpk1p in these mutants showed an elevated level of doubly phosphorylated Mpk1 protein, indicating that the growth defect of rom2 mutants is not due to an inability to activate the MAP kinase module, but rather to lack of a function of the Rom2 protein that has yet to be identified precisely.

Alleles↗
PubMed2001

Lrg1p functions as a putative GTPase-activating protein in the Pkc1p-mediated cell integrity pathway in Saccharomyces cerevisiae.

In Saccharomyces cerevisiae the ROM2 gene encodes a GDP/GTP exchange factor for the small G-protein Rho1p, a known activator of protein kinase C. In a screen designed to isolate suppressors of a rom2 mutant allele, we identified a mutant defective in the gene coding for the putative GTPase-activating protein Lrg1p. This protein was previously suggested to be involved in sporulation and mating. Here we provide evidence for its role in Pkc1p-mediated signal transduction based on the following results. (1) Deletion of LRG1 suppresses the growth phenotypes associated with mutations in SLG1 (which codes for a putative sensor of cell wall damage). (2) Using two-hybrid assays an interaction between the GAP domain of Lrg1p and Rho1p was demonstrated. (3) The lrg1 mutant shows enhanced activity of the Pkc1p pathway. (4) Overexpression of LRG1 leads to a cell lysis defect that can be suppressed by the addition of osmotic stabilizers. Phenotypic comparison of lrg1 mutants with mutants defective in other GTPase-activating proteins (Sac7p, Bem2p, Bag7p) presumed to act on Rho1p revealed that deletion of SAC7, but not BEM2 or BAG7, suppresses the phenotype of rom2 mutants. Pairwise combination of mutations in all these genes showed that the simultaneous deletion of SAC7 and LRG1 is synthetically lethal. We therefore suggest that Lrg1p acts as a negative regulator of the Pkc1p pathway in conjunction with its known homologue Sac7p.

Base Sequence↗
PubMed2000

Use of G-protein fusions to monitor integral membrane protein-protein interactions in yeast.

The control of protein-protein interactions is a fundamental aspect of cell regulation. Here we describe a new approach to detect the interaction of two proteins in vivo. By this method, one binding partner is an integral membrane protein whereas the other is soluble but fused to a G-protein gamma-subunit. If the binding partners interact, G-protein signaling is disrupted. We demonstrate interaction between known binding partners, syntaxin 1a with neuronal Sec1 (nSec1), and the fibroblast-derived growth factor receptor 3 (FGFR3) with SNT-1. In addition, we describe a genetic screen to identify nSec1 mutants that are expressed normally, but are no longer able to bind to syntaxin 1a. This provides a convenient method to study interactions of integral membrane proteins, a class of molecules that has been difficult to study by existing biochemical or genetic methods.

Adaptor Proteins, Signal Transducing↗
PubMed1999

Characterization of KLBCK1, encoding a MAP kinase kinase kinase of Kluyveromyces lactis.

The cellular integrity and response to hypoosmotic conditions in the yeast Saccharomyces cerevisiae are ensured by a MAP kinase signal transduction pathway mediated by the yeast homolog of mammalian protein kinase C. Bck1p functions as the MAP kinase kinase kinase of this pathway. Here we report on the cloning and analysis of the BCK1 homolog from the milk yeast Kluyveromyces lactis (KlBCK1). The deduced protein sequences display three highly conserved domains with the serine/threonine kinase domain containing 89 % identical amino acid residues. Interestingly, a region identified in KlBck1p as a putative SAM domain, mediating protein-protein interactions, is also conserved in ScBck1p. Yet, two-hybrid analyses indicate that this region may not be involved in dimerization of KlBck1p in contrast to its S. cerevisiae counterpart. Expression of KlBCK1 fully complements the defects in a Scbck1 null mutant and is capable of activating the pathway as indicated by a reporter system based on the transcription factor Rlm1p. However, deletion from the haploid K. lactis genome does not result in a loss of cellular integrity under a variety of conditions tested. Thus, despite the functional conservation in this component of the MAP kinase pathway in both yeast, cellular integrity in K. lactis may depend at least in part on different signalling mechanisms when compared with S. cerevisiae.

Amino Acid Sequence↗
PubMed1999

The protein kinase C-mediated MAP kinase pathway involved in the maintenance of cellular integrity in Saccharomyces cerevisiae.

Signal transduction mediated by the single yeast isozyme of protein kinase C (Pkc1p) is essential for the maintenance of cellular integrity in this model eukaryote. The past few years have seen a dramatic increase in our knowledge of the upstream regulatory factors that modulate Pkc1p activity (e.g. Tor2p, Rom1p, Rom2p, Rho1p, Slg1p, Mid2p) and of the downstream targets of the MAP kinase cascade triggered by it (e.g. Rlm1p, SBF complex). The picture that has emerged connects this pathway to a variety of other cellular processes, such as cell cycle progression (Cdc28p, Swi4p), mating (Ste20p), nutrient sensing (Ira1p), calcium homeostasis (calcineurin, Mid2p, Fks2p) and the structural dynamics of the cytoskeleton (Spa1p, Bni1p).

Calcium-Calmodulin-Dependent Protein Kinases↗
PubMed1998

A screen for upstream components of the yeast protein kinase C signal transduction pathway identifies the product of the SLG1 gene.

We employed the constitutive BCK1-20 allele of the gene for the MAP kinase kinase kinase (MAP-KKK) in the yeast Pkc signal transduction pathway to develop a genetic screen for mutants in genes encoding upstream components. Transposon mutagenesis yielded a mutant that was completely dependent on the active allele in the absence of osmotic stabilization. The transposon had integrated at the yeast SLG1 (HCS77) locus. This gene encodes a putative membrane protein. Haploid slg1 deletion strains are sensitive to caffeine, as expected for mutants in the Pkc pathway, as well as a variety of other drugs. The response to elevated temperatures and the dependence on osmotic stabilization depends on the genetic background. Thus, in the strain used for mutagenesis, disruption of SLG1 causes the cells to become non-viable in the absence of osmotic stabilization at both 30 degrees C and 37 degrees C. In a different genetic background this phenotype was not observed. Sensitivity of the haploid deletion mutants to caffeine can be partially suppressed by overexpression of genes for other components of the Pkc pathway, such as PKC1, SLT2, ROM2, and STE20. In addition, a SLG1-lacZ reporter construct shows higher expression in the presence of caffeine or magnesium chloride in a wild-type diploid background.

DNA Transposable Elements↗
PubMed1997

Mutants affected in the putative diacylglycerol binding site of yeast protein kinase C.

In an attempt to study the functional similarities between protein kinase C from the yeast Saccharomyces cerevisiae and its human homologues we have started in vitro mutagenesis to alter specific domains. Here we report on the exchange of four cysteine residues by serines in yeast Pkc1p that have been shown to be essential for diacylglycerol (DAG) binding and activation by this compound in humans. The mutant yeast protein leads to sensitivity to caffeine and low concentrations of SDS when expressed in a pkc1 deletion strain. However, sensitivity to staurosporine was not affected. Our data indicate that the conserved DAG binding domain serves an important function in yeast Pkc1p.

Amino Acid Sequence↗
PubMed1997

Analysis of a transketolase gene from Kluyveromyces lactis reveals that the yeast enzymes are more related to transketolases of prokaryotic origins than to those of higher eukaryotes.

The role of the pentose-phosphate pathway in carbohydrate metabolism of the yeast Kluyveromyces lactis, and the evolutionary relationships between the encoding genes, was investigated. For this purpose, we isolated the gene encoding transketolase (KlTKL1) and determined its nucleotide sequence. Surprisingly, comparisons of the deduced amino-acid sequence with those from other organisms revealed that the yeast enzymes are more related to those from prokaryotic sources than to those from higher eukaryotes. Functional analyses showed that KlTKL1 also complemented a Saccharomyces cerevisiae tkl1 tkl2 double mutant for growth in the absence of aromatic amino acids and restored transketolase activity in this mutant. A band detected in these transformants by Western-blot analysis corresponded to a band detected in K. lactis both in a wild-type strain and in a multicopy transformant with elevated transketolase activity.

Amino Acid Sequence↗