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Biomedical subjects

I Herskowitz

Publications and source records attributed to I Herskowitz.

At least 19 recordsLinked to original sources
PubMed1992

Roles of SWI1, SWI2, and SWI3 proteins for transcriptional enhancement by steroid receptors.

The SWI1, SWI2, and SWI3 proteins, which are required for regulated transcription of numerous yeast genes, were found also to be essential for rat glucocorticoid receptor function in yeast; the receptor failed to activate transcription in strains with mutations in the SWI1, SWI2, or SWI3 genes. Certain mutations in genes encoding components of chromatin, identified as suppressors of swi mutations, partially relieved the SWI- requirement for receptor function. Immunoprecipitation of glucocorticoid receptor derivatives from wild-type (SWI+) yeast extracts coprecipitated the SWI3 protein; such receptor-SWI3 complexes were not detected in swi1- or swi2- mutant strains, implying that a complex of multiple SWI proteins may associate with the receptor. Prior incubation of a Drosophila embryo transcription extract with the yeast SWI3-specific antibody inhibited receptor function in vitro whereas the antibody had no effect if added after initiation complex formation. Thus, positive regulation by the glucocorticoid receptor in vivo and in vitro appears to require its interaction, at an early step, with one or more SWI proteins.

Adenosine Triphosphatases↗
PubMed1992

Cloning of a human galactokinase gene (GK2) on chromosome 15 by complementation in yeast.

A human cDNA encoding a galactokinase (EC 2.7.1.6) was isolated by complementation of a galactokinase-deficient (gal1-) strain of Saccharomyces cerevisiae. This cDNA encodes a predicted protein of 458 amino acids with 29% identity to galactokinase of Saccharomyces carlsbergensis. Previous studies have mapped a human galactokinase gene (GK1) to chromosome 17q23-25, closely linked to thymidine kinase. The galactokinase gene that we have isolated (GK2) is located on chromosome 15. The relationship between the disease locus for galactokinase deficiency galactosemia, which is responsible for cataracts in newborns and possibly presenile cataracts in adults, and the two galactokinase loci is unknown.

Amino Acid Sequence↗
PubMed1992

A yeast gene (BEM1) necessary for cell polarization whose product contains two SH3 domains.

Cell polarization requires that a cellular axis or cell-surface site be chosen and that the cytoskeleton be organized with respect to it. Details of the link between the cytoskeleton and the chosen axis or site are not clear. Cells of the yeast Saccharomyces cerevisiae exhibit cell polarization in two phases of their life cycle, during vegetative growth and during mating, which reflects responses to intracellular and extracellular signals, respectively. Here we describe the isolation of two mutants defective specifically in cell polarization in response to peptide mating pheromones. The mutants carry special alleles (denoted bem1-s) of the BEM1 gene required for cell polarization during vegetative growth. Unlike other bem1 mutants, the bem1-s mutants are normal for vegetative growth. Complete deletion of BEM1 leads to the defect in polarization of vegetative cells seen in bem1 mutants. The predicted sequence of the BEM1 protein (Bem1p) reveals two copies of a domain (denoted SH3) that is found in many proteins associated with the cortical cytoskeleton and which may mediate binding to actin or some other component of the cell cortex. The sequence of Bem1p and the properties of mutants defective in this protein indicate that it may link the cytoskeleton to morphogenetic determinants on the cell surface.

Adaptor Proteins, Signal Transducing↗
PubMed1992

Characterization of the yeast SWI1, SWI2, and SWI3 genes, which encode a global activator of transcription.

The yeast SWI1, SWI2 (SNF2), and SWI3 genes are required for transcription of HO and INO1 genes. We show that they are also required for transcription of ADH1, ADH2, SUC2, GAL1, and GAL10 and for function of simple UAS elements with binding sites for yeast GAL4 or Drosophila ftz proteins. SWI3 encodes a 99 kd nuclear protein containing a large, highly acidic N-terminal domain. SWI1 is identical to ADR6, which encodes a positive regulator of ADH1 and ADH2. Transcription of HO also requires SNF5 and SNF6. These and other observations suggest that SWI1, SWI2, SWI3, SNF5, and SNF6 may be components of a large multi-subunit complex. We propose that these products perform a general role in transcription by assisting gene-specific regulatory proteins.

Amino Acid Sequence↗
PubMed1992

Learning about cancer genes through invertebrate genetics.

Genetic studies in yeast, nematodes and Drosophila are revealing the signal transduction pathways that regulate differentiation and cell proliferation. Some of the critical molecules involved are homologous to proto-oncogenes and others are likely to be analogous to the products of tumor suppressor genes.

Animals↗
PubMed1992

Phosphorylation of FAR1 in response to alpha-factor: a possible requirement for cell-cycle arrest.

Exposure of yeast a cells to alpha-factor causes cells to arrest in the G1 phase of the cell cycle. The FAR1 gene is required for this cell-cycle arrest; its product is necessary for the inhibition of a G1 cyclin, CLN2. Earlier work demonstrated that alpha-factor caused an increase in the transcription of FAR1 severalfold over a measurable basal level. We now show that transcriptional induction of FAR1 from a heterologous promoter is not sufficient to inhibit CLN2 in the absence of alpha-factor. We also show that FAR1 is phosphorylated in response to alpha-factor and propose that this phosphorylation may be required for FAR1 activity.

Base Sequence↗
PubMed1992

The a locus governs cytoduction in Ustilago maydis.

We have developed a cytoduction assay to measure cell fusion quantitatively in the basidiomycete corn smut fungus Ustilago maydis. This assay employs a mutation conferring resistance to oligomycin that exhibits non-Mendelian inheritance and presumably affects the mitochondrial genome. After auxotrophic olir cells are mixed with prototrophic olis cells, prototrophic olir cells can be detected at a significant frequency after several hours of incubation, reaching a maximum of 10% of the total prototrophs in the mixture after 18 h. We demonstrate that this cell fusion event occurs only if the mating partners have different alleles of the a mating-type locus and is not influenced by the b locus. These studies support the view that the a locus but not the b locus controls establishment of the filamentous, pathogenic state.

Cell Fusion↗
PubMed1991

Transcriptional activation of CLN1, CLN2, and a putative new G1 cyclin (HCS26) by SWI4, a positive regulator of G1-specific transcription.

SWI4 of budding yeast codes for a component of a transcription factor (cell cycle box factor, or CCBF) necessary for G1-specific expression of HO. We show that SWI4 is essential for haploid cell viability at high temperature and in a/alpha cells at all temperatures: SWI4-deficient cells arrest as large unbudded cells. Eight high copy number plasmids were identified that allow swi4- strains to grow under nonpermissive conditions. Two carry G1 cyclin genes, CLN1 and CLN2; another carries HCS26, coding for a putative cyclin, a/alpha swi4- mutants exhibit 3- to 20-fold reductions in the levels of CLN1, CLN2, and HCS26 transcripts. The requirement of SWI4 for transcription appears to be direct: each gene contains sites similar to the CCBF-binding site; CCBF binds to the upstream region of HCS26. We propose that SWI4 participates in a positive feedback loop by which CLN1, CLN2, and possibly HCS26 promote their own transcription in G1.

Amino Acid Sequence↗
PubMed1991

Genetic control of bud site selection in yeast by a set of gene products that constitute a morphogenetic pathway.

Yeast cells choose bud sites on their surface in two distinct spatial patterns: axial for a and alpha cells and bipolar for a/alpha cells. We have identified four genes, BUD1-BUD4, necessary for the axial pattern by isolating mutants of alpha cells that do not exhibit this pattern. Mutations in BUD1 (which is the same as the previously identified gene RSR1) or BUD2 lead to a random budding pattern in all cell types; mutations in BUD3 or BUD4 lead to a bipolar pattern in all cell types. These observations indicate the existence of a basal budding pattern, requiring no BUD products, that is random; BUD1 and BUD2 act on this basal pattern to create the bipolar pattern; the further action of BUD3 and BUD4 leads to the axial pattern. These studies thus identify a set of gene products that directs cell morphogenesis to a genetically programmed site.

Animals↗
PubMed1991

Yeast BUD5, encoding a putative GDP-GTP exchange factor, is necessary for bud site selection and interacts with bud formation gene BEM1.

Cells of the yeast S. cerevisiae choose bud sites in an axial or bipolar spatial pattern depending on their cell type. We have identified a gene, BUD5, that resembles BUD1 and BUD2 in being required for both patterns; bud5- mutants also exhibit random budding in all cell types. The BUD5 nucleotide sequence predicts a protein of 538 amino acids that has similarity to the S. cerevisiae CDC25 product, an activator of RAS proteins that catalyzes GDP-GTP exchange. Two potential targets of BUD5 are known: BUD1 (RSR1) and CDC42, proteins involved in bud site selection and bud formation, respectively, that have extensive similarity to RAS. We also show that BUD5 interacts functionally with a gene, BEM1, that is required for bud formation. This interaction provides further support for the view that products involved in bud site selection guide the positioning of a complex necessary for bud formation.

Amino Acid Sequence↗
PubMed1991

A functional interaction between the C-terminal domain of RNA polymerase II and the negative regulator SIN1.

The C-terminal domain (CTD) of the largest subunit of yeast RNA polymerase II contains 26-27 tandem copies of a conserved heptapeptide of unknown function. Yeast strains whose CTD contains ten heptamers are viable but defective for transcription of the INO1 gene and cold sensitive for growth. Deletion of the SIN1 gene, which codes for a DNA-binding protein that negatively regulates HO transcription, restores INO1 transcription and reduces the cold sensitivity of such strains. A SIN1 deletion suppresses the lethality of a CTD with nine heptamer repeats but not with seven repeats. These observations indicate a functional relationship between SIN1 and the CTD: the CTD might remove SIN1 from DNA, or removal of SIN1 may be a prerequisite for function of the CTD. The SWI1, SWI2, and SWI3 genes, whose products activate HO transcription by antagonizing SIN1, are also required for INO1 transcription and may assist the CTD. In addition, an intact CTD binds nonspecifically to DNA in vitro.

Amino Acid Sequence↗
PubMed1991

The yeast RME1 gene encodes a putative zinc finger protein that is directly repressed by a1-alpha 2.

In the yeast Saccharomyces cerevisiae, a/alpha cells can enter meiosis whereas a and alpha cells cannot. The a/alpha cell type is determined by presence of a repressor, a1-alpha 2. Previous studies indicate that a/alpha cells lack an inhibitor of meiosis, the RME1 gene product, and that a and alpha cells express RME1. We report here the sequence of RME1 and functional analysis of its regulatory and coding regions. The 5'-region of RME1 includes a sequence resembling a1-alpha 2 repression sites. Deletion of this site at RME1 relieves repression by a1-alpha 2, and insertion of the site into a heterologous regulatory region (CYC1) confers weak repression in a/alpha cells. These observations indicate that RME1 is directly repressed by a1-alpha 2. The RME1 product has three regions that resemble C2H2 zinc fingers, which are characteristic of a class of nucleic-acid-binding proteins. Substitution of serine for cysteine in each of the putative fingers abolishes RME1 function; serine substitutions in the second and third putative fingers do not affect RME1 stability. These findings indicate that at least two putative zinc fingers are critical for RME1 structure or activity. Therefore RME1, which is formally a negative regulator of the meiotic gene IME1, may act directly as a repressor.

Amino Acid Sequence↗
PubMed1991

A negative regulator of HO transcription, SIN1 (SPT2), is a nonspecific DNA-binding protein related to HMG1.

The SIN1 gene was initially identified because mutations in SIN1 bypass the need for SWI1 to activate transcription of the yeast HO gene. We show here that transcription of HO in swi1 sin1 cells efficiently utilizes the normal start site. We have cloned SIN1 and found that it is identical to the previously identified gene SPT2, mutations in which allow transcription from certain mutated regulatory regions. The predicted SIN1/SPT2 protein has a distinctive amino acid composition (45% charged residues, 25% basic and 20% acidic) and has similarity to the mammalian HMG1 protein, a nonhistone component of chromatin. We show that SIN1 is concentrated in the nucleus and binds to DNA with little or no sequence specificity in vitro. It thus exhibits properties of an HMG protein. Addition of random DNA segments to a test promoter alters regulation by SIN1 in a manner similar to addition of a segment from the HO upstream region. Functional analysis of certain SIN1 mutations suggests that SIN1 may be part of a multiprotein complex. On the basis of these results, we propose that SIN1 is a nonhistone component of chromatin which creates the proper context for transcription. Because sin1 mutants exhibit increased loss of chromosome III, SIN1 may also play a role in fidelity of chromosome segregation.

Amino Acid Sequence↗