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Biomedical subjects

M J Leibowitz

Publications and source records attributed to M J Leibowitz.

At least 55 records · Page 3Linked to original sources
PubMed1985

1,2,4-Triazolo[4,3-a]quinoxaline-1,4-diones as antiallergic agents.

A series of new 1,4-dihydro-1,2,4-triazolo[4,3-]quinoxaline-1,4-diones has been prepared. These compounds were tested as inhibitors of antigen-induced release of histamine (AIR) in vitro from rat peritoneal mast cells (RMC) and as inhibitors of IgE-mediated rat passive cutaneous anaphylaxis (PCA). Most of this new class of antiallergic agents showed good activity in the RMC and PCA tests. The most potent compound, 2-acetyl-7-chloro-5-n-propyl-1,2,4-triazolo[4,3-a]quinoxaline-1,4-dione (1x), with an I50 value of 0.1 microM, is 30 times more potent than disodium cromoglycate (DSCG) in the RMC assay.

Animals↗
PubMed1984

Genome structure and expression of a defective interfering mutant of the killer virus of yeast.

A large internal deletion in M1 double-stranded (ds) RNA from the killer virus of Saccharomyces cerevisiae generates a suppressive (S3) dsRNA molecule. Strains which harbor S3 dsRNA are defective in toxin production and immunity to the toxin. The biochemical defect in expression has been investigated and is apparently due to truncation of the protoxin polypeptide translation reading frame on S3 dsRNA. Transcription in vivo, and in isolated virions in vitro, results in the synthesis of a full-length positive polarity messenger RNA, denoted s. The s transcript contains no long poly(A) tracts as determined by its lack of affinity for oligo(dT)-cellulose, and as inferred by sequence analysis of approximately 87% of the S3 dsRNA genome. These data support a model for template coding of polyadenylate in transcripts derived from the wild-type M1 dsRNA. The orientation of the sequences conserved on S3 dsRNA with respect to M1 dsRNA has been determined. Some of the conserved sequences are likely to be required for the maintenance and replication of these viral dsRNA genomes in S. cerevisiae.

Amino Acid Sequence↗
PubMed1984

Pyrido[3',2':4,5]thieno[3,2-d]-N-triazines: a new series of orally active antiallergic agents.

A new series of orally active mediator release inhibitors, pyrido[3',2':4,5]thieno[3,2-d]-N-triazines, was synthesized and evaluated for antiallergic activity. Several products showed high activity as inhibitors or wheal information in the rat passive cutaneous anaphylaxis screen and as inhibitors of histamine release from passively sensitized rat mast cells. Many compounds were orally active in the PCA test. The most potent compound, 7-phenylpyrido-[3',2':4,5]thieno[3,2-d]-1,2,3-triazin-4(3H)- one (10) with an I50 value of 0.05 microM, was 60 times more potent than disodium cromoglycate (DSCG) in the RMC assay.

Administration, Oral↗
PubMed1984

Saccharomyces cerevisiae killer virus transcripts contain template-coded polyadenylate tracts.

The M double-stranded RNA component of type 1 killer strains of the yeast Saccharomyces cerevisiae contains an internal 200-base pair adenine- and uracil-rich region. The plus strands of this viral genomic RNA contain an internal adenine-rich region which allows these strands to bind to polyuridylate-Sepharose as tightly as do polyadenylated RNAs with 3'-terminal polyadenylated tracts of 70 to 100 residues. Internal template coding of an adenine-rich tract in positive polarity in vivo and in vitro transcripts of M double-stranded RNA may serve as an alternate method of transcript polyadenylation. The 3'-terminal residue of the in vitro m transcript is a non-template-encoded purine residue. The 5' terminus of this transcript is involved in a stem-and-loop structure which includes an AUG initiation codon, along with potential 18S and 5.8S rRNA binding sites. Except for the 3'-terminal residue, transcription in in vitro shows complete fidelity.

Base Sequence↗
PubMed1984

Multiple L double-stranded RNA species of Saccharomyces cerevisiae: evidence for separate encapsidation.

The L double-stranded (ds) RNA component of Saccharomyces cerevisiae may contain up to three dsRNA species, each with a distinct sequence but with identical molecular weights. These dsRNAs have been separated from each other by denaturation and polyacrylamide gel electrophoresis. The 3' terminal sequences of the major species, LA dsRNA, were determined. Secondary structural analysis supported the presence of two stem and loop structures at the 3' terminus of the LA positive strand. In strain T132B NK-3, both the LA and LC species are virion encapsidated. Two distinct classes of virions were purified from this strain, each with a different RNA polymerase activity and with distinct protein components. The heavy virions harbored LA dsRNA, whereas the LC dsRNA species co purified with the light virion peak. Thus, LA and LC dsRNAs, when present in the same cell, may be separately encapsidated.

Base Sequence↗
PubMed1982

Structural and functional analysis of separated strands of killer double-stranded RNA of yeast.

The two strands of the M double-stranded RNA species from a killer strain of Saccharomyces cerevisiae have been separated, and the 3'-terminal sequences of these strands have been determined. The positive strand programs the synthesis of the putative killer toxin precursor (M-p32) in a rabbit reticulocyte in vitro translation system. Only the negative strand hybridizes to the positive polarity transcript (m) synthesized in vitro by the virion-associated transcriptase activity. Secondary structural analysis of the extreme 3'-terminus of the negative strand using S1 nuclease is consistent with the presence of a large stem and loop structure previously proposed on the basis of RNA sequence data. This structure, and a similar structure at the corresponding 5'-terminus of the positive strand, may have functional significance in vivo.

Animals↗
PubMed1982

Separation and sequence of the 3' termini of M double-stranded RNA from killer yeast.

Four subspecies of M double-stranded RNA from a killer strain of Saccharomyces cerevisiae were isolated. Each subspecies were susceptible to heat cleavage, presumably at an internal 190 base pair A,U-rich region, generating two discrete fragments corresponding to each side of the A, U-rich region. Enzymatic and chemical RNA sequence analysis defined the 3'-terminal 175 bases for the larger fragment (M-1) and 231 bases for the smaller fragment (M-2). All four subspecies of M have identical size and 3'-terminal sequences. Potential translation initiation codons are present on the corresponding 5' termini of both fragments, and a possible 18S ribosomal RNA binding site is also present on the 5' terminus of M-1. Stem and loop structures for the 5' and 3' termini of M-1 may function as recognition sites for replication, transcription, and translation.

Amino Acid Sequence↗
PubMed1982

Localization of genes for the double-stranded RNA killer virus of yeast.

The M double-stranded RNA (ds RNA) genome segment of the cytoplasmically inherited killer virus of yeast codes for two polypeptides when denatured and translated in vitro: a previously known 32,000-dalton peptide and a newly discovered 19,000-dalton peptide (NaDodSO4/polyacrylamide gel electrophoresis). An internal 190-base-pair region of the ds RNA is selectively degraded by S1 nuclease treatment at 65 degrees C, resulting in two ds RNA fragments which contain the termini of the original ds RNA. The larger fragment codes for the 32,000-dalton polypeptide and the smaller fragment codes for the 19,000-dalton polypeptide. Thus, the two gene products of M are encoded by distinct regions of this ds RNA.

DNA, Fungal↗
PubMed1980

Virion DNA-independent RNA polymerase from Saccharomyces cerevisiae.

The "killer" plasmid and a larger double-stranded RNA plasmid of yeast exist in intracellular virion particles. Purification of these particles from a diploid killer strain of yeast (grown into stationary growth on ethanol) resulted in co-purification of a DNA-independent RNA polymerase activity. This activity incorporates and requires all four ribonucleoside triphosphates and will not act on deoxyribonucleoside triphosphates. The reaction requires magnesium, is inhibited by sulfhydryl-oxidizing reagents and high concentrations of monovalent cation, but is insensitive to DNase, alpha-amanitin, and actinomycin D. Pyrophosphate inhibits the reaction as does ethidium bromide. Exogenous nucleic acids have no effect on the reaction. The product is mostly single-stranded RNA, some of which is released from the enzymatically active virions.

DNA-Directed RNA Polymerases↗
PubMed1980

Transcription of killer virion double-stranded RNA in vitro.

Intracellular virions of stationary phase ethanol-grown cells of a killer strain of Saccharomyces cerevisiae contain encapsulated M (1.1 x 10(6) dalton) and L (3.2 x 10(6) dalton) double-stranded RNA plasmids. These virions also contain RNA polymerase activity which catalyzes the synthesis of full-length, single-stranded, asymmetric transcripts (denoted m and l) of the virion double-stranded RNAs. Product m is made by M-containing particles and shows complete sequence homology to M but not to L. Product l is made by L-containing particles and shows complete homology only to L. The products show no self-homology, indicating asymmetric transcription. Therefore, the polymerase appears to function in vitro as a double-stranded RNA transcriptase. The lack of sequence homology between M and L is confirmed.

Base Sequence↗
PubMed1979

Mak mutants of yeast: mapping and characterization.

Killer strains of Saccharomyces cerevisiae are those carrying a 1.5 x 10(6)-dalton double-stranded (ds) ribonucleic acid (RNA) (M) in virus-like particles and secreting a protein toxin. Most yeast (koller or not) also carry a 3 x 10(6)-dalton dsRNA (L). We have mapped mutations in eight of the chromosomal genes needed for maintaining M (mak genes). The mak genes are widely distributed on the yeast map, with no multigene complexes. We show that mutants defective in these and other mak genes lose M dsRNA, but not L dsRNA. The mak3-1 mutation results in markedly decreased cellular levels of L dsRNA, but mak3-1 stains do not lose L dsRNA completely. Mutation of mak16 results in temperature-sensitive growth, whereas mutations in mak13, mak15, mak17, mak20, mak22, and mak27 result in slow growth at any temperature. No effect of mak mutations on mating, meiosis, sporulation, germination, homothallism, or ultraviolet sensitivity has been found. The specificity of mak mutations is discussed.

Chromosome Mapping↗
PubMed1978

Pet18: a chromosomal gene required for cell growth and for the maintenance of mitochondrial DNA and the killer plasmid of yeast.

Mutations in the pet18 gene of Saccharomyces cerevisiae (formerly denoted pets) confer three phenotypes on mutant strains: (i) inability to respire (petite), (ii) inability to maintain the double-stranded RNA killer plasmid (sensitive), and (iii) temperature sensitivity for growth. We find that pet18 mutants lack mitochondrial DNA. However, despite their inability to maintain the killer RNA plasmid and mitochondrial DNA, pet18 mutants still can carry the other yeast plasmids, [URE3--1], [PSI], and 2-micron DNA. The temperature sensitivity of the pet18 mutants is not expressed as a selective defect in total DNA, RNA, or protein synthesis.

DNA, Mitochondrial↗
PubMed1976

Two chromosomal genes required for killing expression in killer strains of Saccharomyces cerevisiae.

The killer character of yeast is determined by a 1.4 X 10(6) molecular weight double-stranded RNA plasmid and at least 12 chromosomal genes. Wild-type strains of yeast that carry this plasmid (killers) secret a toxin which is lethal only to strains not carrying this plasmid (sensitives).--We have isolated 28 independent recessive chromosomal mutants of a killer strain that have lost the ability to secrete an active toxin but remain resistant to the effects of the toxin and continue to carry the complete cytoplasmic killer genome. These mutants define two complementation groups, kex1 and kex2. Kex1 is located on chromosome VII between ade5 and lys5. Kex2 is located on chromosome XIV, but it does not show meiotic linkage to any gene previously located on this chromosome.--When the killer plasmid of kex1 or kex2 strains is eliminated by curing with heat or cycloheximide, the strains become sensitive to killing. The mutant phenotype reappears among the meiotic segregants in a cross with a normal killer. Thus, the kex phenotype does not require an alteration of the killer plasmid.--Kex1 and kex2 strains each contain near-normal levels of the 1.4 x 10(6) molecular weight double-stranded RNA, whose presence is correlated with the presence of the killer genome.

Chromosome Mapping↗
PubMed1976

A chromosomal gene required for killer plasmid expression, mating, and spore maturation in Saccharomyces cerevisiae.

"Killer" strains of Saccharomyces cerevisiae are those that harbor a double-stranded RNA plasmid and secrete a toxin that kills only strains not carrying this plasmid (sensitives). Two chromosomal genes (kex1 and kex2) are required for the secretion of toxin by plasmid-carrying strains. The kex2 gene, which maps at a site distinct from the mating-type locus, is also required for normal mating by alpha strains and meiotic sporulation in all strains. Strains that are alpha mating-type and kex2 fail to secrete the pheromone alpha-factor or to respond to the alpha-factor II pheromone which causes a morphological change, but they do respond to alpha-factor I which causes G1 arrest in alpha cells. Strains that are alpha mating-type and kex2 show no defect in mating; pheromone secretion, or response to alpha-factor. Diploids that are homozygous for the kex2 mutation, unlike wildtype or heterozygous diploids, fail to undergo sporulation, with the defect occurring in the final spore maturation stage. These same defects in the sexual cycle are present in all kex2 mutants independent of the presence of the "killer" plasmid.

Animals↗