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A Nasim

Publications and source records attributed to A Nasim.

At least 73 records · Page 4Linked to original sources
PubMed1986

Involvement of ras in sexual differentiation but not in growth control in fission yeast.

The function of the ras gene of Schizosaccharomyces pombe has been studied by constructing null and activated alleles of this gene. An activated allele (Val (12)) inhibits conjugation but has no effect on cell growth, entry into stationary phase or sporulation. The phenotype of Val (12) is distinct from that caused by elevating the intracellular level of cAMP. This supports the hypothesis that ras of fission yeast does not modulate adenylate cyclase in a manner analogous to S. cerevisiae RAS. Introduction of a human ras sequence into fission yeast cells containing a non-functional null allele of ras restored the sexual differentiation process thus indicating that the human sequence can complement S. pombe ras. Our data suggest that although ras genes are highly conserved across a considerable evolutionary divide, the cellular function of the ras gene product varies in different organisms.

Journal Article↗
PubMed1986

Allelism within the DEX and STA gene families in Saccharomyces diastaticus.

Saccharomyces diastaticus produces an extracellular glucoamylase and is therefore capable of hydrolyzing and fermenting starch. Tamaki (1978) studied starch utilization in S. diastaticus and found three polymeric genes controlling this function: STA1, STA2 and STA3. Independently, Erratt and Stewart (1978) studied dextrin utilization by the yeast S. diastaticus and designated the gene, which they identified, DEX1. Erratt and Stewart (1981 a, b) later described two other genes which controlled glucoamylase production in S. diastaticus: DEX2 and a third which was allelic to STA3. At that time STA1 and STA2 were not available to test for allelism in the DEX gene family. In this study strains containing the remaining 4 genes have been examined to determine if further allelism exists between the two gene families. It was ascertained that DEX1 is allelic to STA2 and DEX2 is allelic to STA1. Therefore, no new gene controlling starch utilization has been identified and these two nomenclatures can now be consolidated into one. Based on the fact that the glucoamylase from S. diastaticus can hydrolyze both dextrin and starch, dextrin being the term used to describe partially hydrolyzed starch, and the more wide use of the nomenclature STA, we propose to retain STA as the designation for genes coding for glucoamylase production in S. diastaticus.

Alleles↗
PubMed1986

The cloning and characterization of a RAS gene from Schizosaccharomyces pombe.

We have cloned and determined the complete nucleotide sequence of a RAS gene from the yeast Schizosaccharomyces pombe (SP-RAS). The putative RAS protein of 214 amino acids is encoded by two noncontiguous reading frames separated by an intron of 86 bp. The SP-RAS gene product shares extensive homology with the proteins of the Saccharomyces cerevisiae (SC), Dictyostelium, Drosophila, and human RAS genes in its N-terminal region but not in its C-terminal region. The extended C-terminal regions found in the SC-RAS genes have no counterpart in the SP-RAS gene. Thus the RAS genes of these two yeasts are structurally quite distinct. The SP-RAS sequence was expressed in vivo.

Base Sequence↗
PubMed1986

Cloning and expression of a Saccharomyces diastaticus glucoamylase gene in Saccharomyces cerevisiae and Schizosaccharomyces pombe.

A recombinant plasmid pool of the Saccharomyces diastaticus genome was constructed in plasmid YEp13 and used to transform a strain of Saccharomyces cerevisiae. Six transformants were obtained which expressed amylolytic activity. The plasmids each contained a 3.9-kilobase (kb) BamHI fragment, and all of these fragments were cloned in the same orientations and had identical restriction maps, which differed from the map of the STA1 gene (I. Yamashita and S. Fukui, Agric. Biol. Chem. 47:2689-2692, 1983). The glucoamylase activity exhibited by all S. cerevisiae transformants was approximately 100 times less than that of the donor strain. An even lower level of activity was obtained when the recombinant plasmid was introduced into Schizosaccharomyces pombe. No expression was observed in Escherichia coli. The 3.9-kb BamHI fragment hybridized to two sequences (4.4 and 3.9 kb) in BamHI-digested S. diastaticus DNA, regardless of which DEX (STA) gene S. diastaticus contained, and one sequence (3.9 kb) in BamHI-digested S. cerevisiae DNA. Tetrad analysis of crosses involving untransformed S. cerevisiae and S. diastaticus indicated that the 4.4-kb homologous sequence cosegregated with the glucoamylase activity, whereas the 3.9-kb fragment was present in each of the meiotic products. Poly(A)+ RNA fractions from vegetative and sporulating diploid cultures of S. cerevisiae and S. diastaticus were probed with the 3.9-kb BamHI fragment. Two RNA species, measuring 2.1 and 1.5 kb, were found in both the vegetative and sporulating cultures of S. diastaticus, whereas one 1.5-kb species was present only in the RNA from sporulating cultures of S. cerevisiae.

Cloning, Molecular↗
PubMed1985

Replicating instabilities in yeast: occurrence in different mutational systems.

Following mutagenesis of yeast cells with nitrosoguanidine, primary mosaic colonies exhibiting prototrophic/auxotrophic phenotypes were obtained. Upon replating of these primary mosaics, numerous secondary mosaics were present in the progeny. This study shows that replicating instabilities occur at many different loci within the Schizosaccharomyces pombe genome. In addition, the ade-1 gene of Saccharomyces cerevisiae (causing red pigmentation) was used to show that the phenomenon also occurs in this yeast.

Ascomycota↗
PubMed1985

Glucanase gene diversity in prokaryotic and eukaryotic organisms.

A number of bacteria and eukaryotes produce extracellular enzymes that degrade various types of polysaccharides including the glucans starch, cellulose and hemicellulose (xylan). The similarities in the modes of expression and specificity of enzyme classes, such as amylase, cellulose and xylanase, suggest common genetic origins for particular activities. Our determination of the extent of similarity between these glucanases suggests that such data may be of very limited use in describing the early evolution of these proteins. The great diversity of these proteins does allow identification of their most highly conserved (and presumably functionally important) regions.

Amino Acid Sequence↗
PubMed1984

The effect of spermine on spontaneous and UV-induced mutations in Schizosaccharomyces pombe.

The effect of different concentrations of spermine on spontaneous and UV-induced mutation in the adenine forward mutation system of Schizosaccharomyces pombe was investigated. The effect of spermine on spontaneous mutation was studied in 5 mutator strains (mut 1-4, mut 1-23, mut 2-9, mut 2-20 and mut 3-21) and on UV-induced mutation in a pigmented adenine-requiring strain and its radiation-sensitive derivative (rad 13). The effect of spermine exposure on mutation induction before and after UV irradiation was also investigated. Spermine increased spontaneous forward mutation in the mut 1-4 strain by 47%, and enhanced UV-induced forward mutation 2-fold in the rad 13 and normal pigmented strains. No antimutagenic effect of spermine was seen in any of the strains tested. This is in marked contrast to the antimutagenic effect of spermine observed with bacteria.

Ascomycota↗
PubMed1982

Differential survival as an indicator of potential mutagenicity using repair deficient strains of Saccharomyces cerevisiae and Schizosaccharomyces pombe.

A method is presented to screen chemicals for potential mutagenicity on the basis of their ability to cause more killing in cells of repair-deficient yeast than in wild type cells. Two species were chosen in the event that one might be more sensitive to certain chemicals. The strains used were RAD+ and rad6 derivatives of Saccharomyces cerevisiae and RAD+ and rad3 derivatives of Schizosaccharomyces pombe. This report describes the test system and results for 12 known, direct-acting mutagens (i.e., not requiring mammalian metabolic activation). These compounds showed more lethality in one or both of the repair-deficient strains, indicating that they induce damage to DNA which is subject to repair in wild type cells. Advantages of this system include the use of eukaryotic yeast cells which can be manipulated as easily as bacteria, and that exogenous enzymes (S9) can be added for metabolic activation. Growing yeast cells can activate certain promutagens, and preliminary experiments showed positive responses for diethylnitrosamine and 2-acetylaminofluorene without the addition of S9.

Ascomycota↗
PubMed1981

Pure and mosaic clones--a reflection of differences in mechanisms of mutagenesis by different agents in Saccharomyces cerevisiae.

The induction of pure and mosaic clones has been studied in haploid G1 cells of Saccharomyces cerevisiae. Following treatments with ultraviolet light, methyl methanesulfonate, ethyl methanesulfonate, nitrous acid, and N-methyl-N'-nitro-N-nitrosoguanidine, the relative proportions of pure mutant clones varied from 25 to 100% at comparable survival levels. Ultraviolet light and methyl methanesulfonate produced mainly pure mutant clones, whereas ethyl methanesulfonate and nitrous acid produced mainly mosaics at 59 to 100% survival levels. The ratio of pure to mosaic clones induced by nitrosoguanidine fell between these two classes. These results are consistent with a classification of mutagens on the basis of repair and replication-dependent mechanisms of mutagenesis in other organisms. Agents having actions similar to ultraviolet light may produce mainly pure clones through a pre-replicative process involving an error-prone DNA repair process. Others may produce mainly mosaic mutants due to the different nature of DNA lesions which may require a replication-dependent process for fixation of mutations. Preliminary data from combined treatments of mutagens belonging to two different classes (i.e. ultraviolet light and nitrous acid) suggest the possibility of an interaction between these agents, resulting in a higher proportion of pure clones, possibly due to an inducible process. Studies of induced frequencies of pure and mosaic clones may be useful in the characterization of mutagens with functional differences.

DNA Repair↗
PubMed1981

Production of protoplasts in different yeasts by mutanase.

Mutanase (Mutanase Novo) affects the high frequency production of protoplasts in the following strains of yeast: Saccharomyces cerevisiae, Schizosaccharomyces pombe, Kluyveromyces lactis, Trichosporon pullulans, and Schwanniomyces alluvius. Regeneration frequencies varied with the strain used and ranged between 10 and 18%. This enzyme preparation appears to be a very useful means of obtaining protoplasts from a wide variety of yeasts currently being used for experimental purposes.

Cell Wall↗
PubMed1981

Genetic activity of actinomycin D in Saccharomyces cerevisiae but not in Escherichia coli.

The potential of actinomycin D for induction of forward mutation (ADE-), reversion (TRP+), gene conversion, and mitotic recombination, was examined using haploid and diploid strains of yeast Saccharomyces cerevisiae. No increase in forward or reverse mutations or gene conversion was detected, but actinomycin D induced up to 13-fold increases in mitotic recombinants and a 2-fold increase in numbers of aberrant colonies, in a non-selective assay for genetic activity. Actinomycin D was non-mutagenic in a fluctuation test using Escherichia coli strain WP2 UvrA-. This furnishes an example of a mutagen which is negative in bacteria but has genetic activity in yeast, emphasizing the need for using a battery of microbial tests for determining the genetic activity of any given chemical.

Dactinomycin↗
PubMed1979

Genetic effects of acridine compounds.

Acridines and a very large number of acridine derivatives are used in enormous quantities both in medicine and industry. The mutagenic action of these compounds has been demonstrated in a wide variety of organisms and is known to occur both in the dark as well as in the presence of light (photodynamic action). At the molecular level, acridines have been shown to cause frameshift mutations of both the addition and deletion types, a characteristic which has been of tremendous help in elucidating the nature of the genetic code. These and various other biological effects of acridines, such as inhibition of DNA repair, curing of plasmids and cell-growth inhibition, are examined in this review.

Acridines↗
PubMed1979

Cross sensitivity of mutator strains to physical and chemical mutagens.

Ten different mutator strains of Saccharomyces cerevisiae were tested for cross sensitivity to two alkylaitng agents, ethylmethanesulfonate (EMS) and methylmethanesulfonate (MMS), to determine if any of them are defective in the repair systems which normally deal with damage caused by these agents. For one of the mutators, namely mut2-1, it was shown by genetic analysis that mutator activity and MMS sensitivity are both controlled by the same gene. Two mutants, mut2-1 and mut7-1, were found to be sensitive to MMS but normal to ultraviolet and gamma-rays. Another group is represented by mut1, mut6 and mut8 which are not sensitive to any of the mutagens tested so far. Mutator strain mut2-1 was also shown not to be significantly altered for levels of UV-induced forward and reverse mutations. These observations lend support to the idea of multiple repair systems that deal with DNA damage caused by different agents and also show that mutator activity can often result from the loss of normal cellular repair systems.

DNA Repair↗
PubMed1978

Genetic activity of bleomycin: differential effects on mitotic recombination and mutations in yeast.

The genetic effects of the antitumor antibiotic, bleomycin were studied in different strains of Saccharomyces cerevisiae. It was observed that the drug induced a high frequency of mitotic recombination and gene conversion. In contrast, it produced only a few mutations from adenine independence to adenine dependence and histidine dependence (a missense mutant) to histidine independence. In the strains carrying ochre-suppressible auxotrophic markers, no prototrophs were induced by this drug. The results indicating the specific activity of bleomycin are discussed and, in this connection, the usefulness of yeast as a test organism in mutagenicity screening is emphasized.

Alleles↗