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Biomedical subjects

I Herskowitz

Publications and source records attributed to I Herskowitz.

At least 91 records · Page 5Linked to original sources
PubMed1990

The b alleles of U. maydis, whose combinations program pathogenic development, code for polypeptides containing a homeodomain-related motif.

U. maydis is a fungal pathogen of corn with two forms: one is yeast-like and nonpathogenic; the other is filamentous and pathogenic. The b locus, with 25 different alleles, regulates this dimorphism: any combination of two different alleles triggers pathogenic development, whereas the presence of identical alleles results in the yeast-like form. We have cloned four b alleles (b1, b2, b3, and b4) and show that the b locus contains a single open reading frame (ORF) of 410 amino acids with a variable N-terminal region and a highly conserved C-terminal region (60% and 93% identity, respectively). Mutational analysis confirms that this ORF is responsible for b activity. The b polypeptides appear to be DNA binding proteins because they contain a motif related to the homeodomain in their constant region. We propose that combinatorial interactions between b polypeptides generate regulatory proteins that determine the developmental program of the fungus.

Alleles↗
PubMed1990

CDC36 and CDC39 are negative elements in the signal transduction pathway of yeast.

Mutations in either the CDC36 or CDC39 gene cause yeast cells to arrest in G1 of the cell cycle at the same point as treatment with mating pheromone. We demonstrate here that strains harboring temperature-sensitive mutations in CDC36 or CDC39 activate expression of the pheromone-inducible gene FUS1 when shifted to nonpermissive temperature. We show further that cell-cycle arrest and induction of FUS1 are dependent on known components of the mating factor response pathway, the STE genes. Thus, the G1-arrest phenotype of cdc36 and cdc39 mutants results from activation of the mating factor response pathway. The CDC36 and CDC39 gene products behave formally as negative elements in the response pathway: they are required to block response in the absence of pheromone. Epistasis analysis of mutants defective in CDC36 or CDC39 and different STE genes demonstrates that activation requires the response pathway G protein and suggests that CDC36 and CDC39 products may control synthesis or function of the G alpha subunit.

G1 Phase↗
PubMed1990

The Saccharomyces cerevisiae SIN3 gene, a negative regulator of HO, contains four paired amphipathic helix motifs.

The SIN3 gene (also known as SDI1) is a negative regulator of the yeast HO gene. Mutations in SIN3 suppress the requirement for the SWI5 activator for expression of the yeast HO gene and change the normal asymmetric pattern of HO expression in mother and daughter cells. Furthermore, the in vitro DNA-binding activity of several DNA-binding proteins is reduced in extracts prepared from sin3 mutants. We have cloned the SIN3 gene and determined that a haploid strain with a SIN3 gene disruption is viable. We determined the sequence of the SIN3 gene, which is predicted to encode a 175-kDa polypeptide with four paired amphipathic helix motifs. These motifs have been identified in the myc family of helix-loop-helix DNA-binding proteins and in the TPR family of regulatory proteins. The SIN3 transcript was mapped, and it was determined that the SIN3 transcript was absent in stationary-phase cells. Immunofluorescence microscopy with anti-SIN3 antibody demonstrated that SIN3 protein was present in nuclei. A comparison of restriction map and sequence data revealed that SIN3 is the same as regulatory genes UME4 and RPD1.

Amino Acid Sequence↗
PubMed1989

A regulatory hierarchy for cell specialization in yeast.

The specialized sets of genes that determine different cell types in yeast are controlled by combinations of DNA-binding proteins some of which are present only in certain cell types whereas others are present in all cell types. Final differentiation requires an inductive signal that triggers both gene transcription and cell-cycle arrest. Synthesis of the proteins coded by the 'master regulatory' mating-type locus is regulated so as to generate a heterogeneous mitotic cell population containing a stem-cell lineage.

Fungal Proteins↗
PubMed1989

The yeast SWI4 protein contains a motif present in developmental regulators and is part of a complex involved in cell-cycle-dependent transcription.

Transcription of the HO gene of Saccharomyces cerevisiae, which encodes a site-specific endonuclease that initiates cell-type switching (reviewed in refs. 1,2), is restricted to a short window of the cell cycle in late G1 (refs 3,4). A repeated element in the upstream region of HO (the cell-cycle box, CCB) and two regulatory proteins, SWI4 and SWI6, are required for cell-cycle-dependent expression of HO. Biochemical experiments have identified a factor, CCBF (cell-cycle box factor), that binds to the CCB elements and that presumably plays a key part in cell-cycle regulation of HO. The SWI4 and SWI6 genes are required for formation of the CCBF-DNA complex. Here we report the nucleotide sequence of the SWI4 gene and show that it contains two copies of the conserved SWI6-cdc10 motif observed in SWI6 of budding yeast, the Schizosaccharomyces pombe cdc10 gene required for progression through G19, the Drosophila Notch gene, and in the Caenorhabditis elegans lin-12 and glp-1 genes. We demonstrate by using antibodies to the SWI4 protein in gel-shift assays that the protein is present in the CCBF-DNA complex.

Amino Acid Sequence↗
PubMed1989

Identification of a DNA binding factor involved in cell-cycle control of the yeast HO gene.

Transcription of the HO gene is controlled by at least eleven trans-acting regulators, which are responsible for limiting expression to mother cells and to one period in the cell cycle. A subset of these regulators and a repeated element (the cell-cycle box, CCB) are required for expression of HO during late G1. We describe gel retardation and footprinting experiments that identify a factor, CCBF (cell-cycle box factor), that binds to multiple cell-cycle box elements. We show that the SWI4 and SWI6 genes are required for formation of the CCBF-promoter complex in vitro, either as components of CCBF or as modulators of CCBF activity. The other SWI genes (SWI1, 2, 3, and 5) are not required. We also show that SWI4 and SWI6 are the only SWI genes required for expression in vivo from the CCB sequences. These observations indicate that the CCBF is responsible for cell-cycle regulation of HO and lead to the view that two of the SWI genes, SWI4 and SWI6, are specifically involved in this regulatory event.

Base Sequence↗
PubMed1989

Different a alleles of Ustilago maydis are necessary for maintenance of filamentous growth but not for meiosis.

Two loci (the incompatibility or mating type loci), a and b, govern the life cycle of Ustilago maydis, a fungal pathogen of corn. U. maydis diploids heterozygous at both a and b (a[unk] b[unk]) form mycelial colonies (Fuz(+) phenotype), induce tumors, and produce teliospores able to undergo meiosis. We report here the isolation and characterization of nonmycelial (Fuz(-)) derivatives. These Fuz(-) diploids have allowed us to examine the requirement of a[unk] and b[unk] in maintenance of filamentous growth and tumor-inducing ability. The Fuz(-) diploids are of four classes: two are inferred to be homozygous for b (a[unk] b=); the other two are shown to be homozygous for a (a= b[unk]). These observations confirm the requirement for b[unk] and reveal the requirement for a[unk] in filamentous growth. U. maydis is thus like other basidiomycetes that have two loci governing growth of the dikaryotic filament. The mating behavior of the Fuz(-) diploids indicates that heterozygosity at a or b does not block mating. Although both a= b[unk] and a[unk] b= diploids are nonmycelial, they differ in that a[unk] b= diploids are nonpathogenic, whereas a= b[unk] diploids are pathogenic and produce teliospores able to undergo meiosis. These findings substantiate previous, more limited observations. They demonstrate that ability to induce tumors and produce normal teliospores requires different alleles at b but not at a.

Journal Article↗
PubMed1988

STE2 protein of Saccharomyces kluyveri is a member of the rhodopsin/beta-adrenergic receptor family and is responsible for recognition of the peptide ligand alpha factor.

We have cloned the gene for the alpha-factor receptor of the yeast Saccharomyces kluyveri by using the Saccharomyces cerevisiae receptor gene (c-STE2) as a probe. The nucleotide sequence of the S. kluyveri gene (k-STE2) shows that its predicted polypeptide contains seven hydrophobic segments capable of spanning a lipid bilayer and thus that, like c-STE2, it appears to be a member of the rhodopsin/beta-adrenergic receptor family. The k-STE2 polypeptide is 50% identical to that coded by c-STE2, with high conservation (greater than 67%) in the putative membrane-spanning domains. The carboxyl-terminal amino acid sequences are not similar, but both are very hydrophilic and rich in serine and threonine residues. The k-STE2 gene is functional in S. cerevisiae: it reverses the mating defect of an S. cerevisiae mutant defective in its STE2 gene. S. cerevisiae strains expressing k-STE2 rather than c-STE2 exhibit the mating-factor selectivity characteristic of S. kluyveri: better response to S. kluyveri alpha factor than to S. cerevisiae alpha factor. (S. cerevisiae normally responds much better to its own alpha-factor peptide than to the related alpha-factor peptide of S. kluyveri.) This observation demonstrates that the STE2 gene is responsible for ligand selectivity and provides additional evidence that the STE2 protein is the receptor for alpha factor.

Amino Acid Sequence↗
PubMed1988

The a-factor pheromone of Saccharomyces cerevisiae is essential for mating.

The Saccharomyces cerevisiae pheromone a-factor is produced by a cells and interacts with alpha cells to cause cell cycle arrest and other physiological responses associated with mating. Two a-factor structural genes, MFA1 and MFA2, have been previously cloned with synthetic probes based on the a-factor amino acid sequence (A. Brake, C. Brenner, R. Najarian, P. Laybourn, and J. Merryweather, cited in M.-J. Gething [ed.], Protein transport and secretion, 1985). We have examined the function of these genes in a-factor production and mating by construction and analysis of chromosomal null mutations. mfa1 and mfa2 single mutants each exhibited approximately half the wild-type level of a-factor activity and were proficient in mating, whereas the mfa1 mfa2 double mutant produced no a-factor and was unable to mate. These results demonstrate that both genes are functional, that each gene makes an equivalent contribution to the a-factor activity and mating capacity of a cells, and that a-factor plays an essential role in mating. Strikingly, exogenous a-factor did not alleviate the mating defect of the double mutant, suggesting that an a cell must be producing a-factor to be an effective mating partner.

Amino Acid Sequence↗
PubMed1987

Activation of the yeast HO gene by release from multiple negative controls.

Transcription of the yeast HO gene requires five genes, SWI 1, 2, 3, 4, 5. We present evidence that some SWI products activate HO by antagonizing negative regulatory activities encoded by the SIN genes. sin- mutants (defining six genes) were identified because they express HO in the absence of particular SWI products. We argue that SWI5 activates HO by antagonizing SIN3 and that SWI4 activates HO by antagonizing SIN6. HO is expressed in sin3- daughter cells, hence we infer that the SIN3 product represses HO in wild-type daughter cells and that SWI5 and SIN3 are responsible for the cell-lineage-dependent expression of HO. HO is transcribed only when all types of repression are absent: in mother cells, where SWI5 antagonizes SIN3; in late G1, when SWI4 antagonizes SIN6; and in a or alpha cells, where a1-alpha 2 repression is absent.

Chromosome Deletion↗
PubMed1987

STE16, a new gene required for pheromone production by a cells of Saccharomyces cerevisiae.

Genes required for mating by a and alpha cells of Saccharomyces cerevisiae (STE, "sterile," genes) encode products such as peptide pheromones, pheromone receptors, and proteins responsible for pheromone processing. a-specific STE genes are those required for mating by a cells but not by alpha cells. To identify new a-specific STE genes, we have employed a novel strategy that enabled us to determine if a ste mutant defective in mating as a is also defective in mating as alpha without the need to do crosses. This technique involved a strain (K12-14b) of genotype mata1 HML alpha HMR alpha sir3ts, which mates as a at 25 degrees and as alpha at 34 degrees. We screened over 40,000 mutagenized colonies derived from K12-14b and obtained 28 a-specific ste mutants. These strains contained mutations in three known a-specific genes--STE2, STE6 and STE14--and in a new gene, STE16. ste16 mutants are defective in the production of the pheromone, a-factor, and exhibit slow growth. Based on the distribution of a-specific ste mutants described here, we infer that we have identified most if not all nonessential genes that can give rise to a-specific mating defects.

Crosses, Genetic↗
PubMed1987

Four genes responsible for a position effect on expression from HML and HMR in Saccharomyces cerevisiae.

Mating type interconversion in Saccharomyces cerevisiae occurs by transposition of copies of the a or alpha mating type cassettes from inactive loci, HML and HMR, to an active locus, MAT. The lack of expression of the a and alpha genes at the silent loci results from repression by trans-acting regulators encoded by SIR (Silent Information Regulator) genes. In this paper we present evidence for the existence of four SIR genes. Inactivation of any of these genes leads to expression of cassettes at both HML and HMR. Unusual complementation properties are observed for a number of sir mutations. Specifically, some recessive mutations in different genes fail to complement. The correspondence between SIR1, SIR2, SIR3, SIR4 and other genes with similar roles (MAR, CMT, STE8 and STE9) is presented.

Alleles↗