bluuebunny/crossref_metadata_2025_split huggingface dataset:
Isolation and characterization of mutants constitutive for expression of the fbp1 gene of Schizosaccharomyces pombe.
Authors: Hoffman C S , Winston F 
Published: January 2021

Abstract
Transcription of the fbp1 gene of Schizosaccharomyces pombe, encoding fructose-1,6-bisphosphatase, is glucose repressible. We have constructed two hybrid genes, containing the fbp1 promoter, that allow selection for mutations that alter transcriptional regulation of fbp1. Strains carrying fbp1-ura4 and fbp1-lacZ fusions are phenotypically Ura-, resistant to 5-fluoro-orotic acid, and express a low level of beta-galactosidase activity when grown under repressing conditions (8% glucose). By selecting for Ura+ strains grown under repressing conditions, we have isolated 187 independent mutants that constitutively express the fbp1-ura4 fusion. These mutants identify ten complementation groups that represent ten unlinked git (glucose insensitive transcription) genes. The git gene products are required in trans for glucose repression of expression from the fbp1 promoter since these mutations also alter expression of the fbp1-lacZ fusion. We have shown that transcription of the wild type fbp1 gene in most git mutants is elevated to a level consistent with the increased expression of the fbp1-lacZ hybrid gene. Mutations in some git genes confer additional phenotypes such as slow growth, temperature-sensitive lethality and reduced spore viability. Therefore, some of these genes are likely to encode factors that are of general importance for S. pombe transcription.
Recent appearance and molecular characterization of mitochondrial DNA deletions within a defined nematode pedigree.
Authors: Hyman B C , Slater T M 
Published: January 2021

Abstract
The mitochondrial genome of Romanomermis culicivorax, a parasitic nematode of mosquitoes, contains an amplified 3.0-kilobase (kb) locus organized as direct repeats and as noncontiguous, inverted copies. These amplified sequences are actively undergoing rearrangement. One recent event has resulted in a 1133-base pair (bp) deletion located entirely within a single amplified segment. The deletion junction occurs between two imperfect 58-bp repeats, implicating strand pairing in this alteration. A second event has generated mitochondrial DNA (mtDNA) forms differing by a single, intact 3.0-kb repeating unit. By analyzing molecules derived from independently reared subcultures, it appears these new mtDNA forms arose within the last 170 nematode generations. Our results indicate that the occurrence and selection of novel animal mitochondrial genomes can now be studied in this experimentally manipulable nematode system.
Developmental expression of the glucose dehydrogenase gene in Drosophila melanogaster.
Authors: Cox-Foster D L , Schonbaum C P , Murtha M T , Cavener D R 
Published: January 2021

Abstract
The Gld gene of Drosophila melanogaster is transiently expressed during every stage of development. The temporal pattern of Gld expression is highly correlated with that of ecdysteroids. Exogeneous treatment of third instar larvae with 20-hydroxyecdysone induces the accumulation of Gld mRNA in the hypoderm and anterior spiracular gland cells. During metamorphosis Gld is expressed in a variety of tissues derived from the ectoderm. In the developing reproductive tract, Gld mRNA accumulates in the female spermathecae and oviduct and in the male ejaculatory duct and ejaculatory bulb. These four organs are derived from closely related cell lineages in the genital imaginal disc. Since the expression of Gld is not required for the development of these reproductive structures, this spatial pattern of expression is most likely a fortuitous consequence of a shared regulatory factor in this cell lineage. At the adult stage a high level of the Gld mRNA is only observed in the male ejaculatory duct.
Genetic analysis of the adenosine3 (Gart) region of the second chromosome of Drosophila melanogaster.
Authors: Tiong S Y , Nash D 
Published: January 2021

Abstract
The Gart gene of Drosophila melanogaster is known, from molecular biological evidence, to encode a polypeptide that serves three enzymatic functions in purine biosynthesis. It is located in polytene chromosome region 27D. One mutation in the gene (ade3(1)) has been described previously. We report here forty new ethyl methanesulfonate-induced mutations selected aga!nst a synthetic deficiency of the region from 27C2-9 to ++28B3-4. The mutations were characterized cytogenetically and by complementation analysis. The analysis apparently identifies 12 simple complementation groups. In addition, two segments of the chromosome exhibit complex complementation behavior. The first, the 28A region, gave three recessive lethals and also contains three known visible mutants, spade (spd), Sternopleural (Sp) and wingless (wg); a complex pattern of genetic interaction in the region incorporates both the new and the previously known mutants. The second region is at 27D, where seven extreme semilethal mutations give a complex complementation pattern that also incorporates ade3(1). Since ade3(1) is defective in one of the enzymatic functions encoded in the Gart gene, we assume the other seven also affect the gene. The complexity of the complementation pattern presumably reflects the functional complexity of the gene product. The phenotypic effects of the mutants at 27D are very similar to those described for ade2 mutations, which also interrupt purine biosynthesis.
Interactions of vestigial and scabrous with the Notch locus of Drosophila melanogaster.
Authors: Rabinow L , Birchler J A 
Published: January 2021

Abstract
Interactions are described between the Notch locus of Drosophila melanogaster, and two other loci, scabrous and vestigial, which respectively affect the eyes and wings. The Notch locus is responsible for mediating decisions of cell fate throughout development in many different tissues. Mutations and duplications of vestigial and scabrous alter the severity of phenotypes associated with Notch mutations and duplications in a manner that is essentially tissue- and allele-specific. These interactions indicate that the products of vestigial and scabrous act in conjunction with Notch to stimulate the differentiation of specific cell types.
Mutations in polycombeotic, a Drosophila polycomb-group gene, cause a wide range of maternal and zygotic phenotypes.
Authors: Phillips M D , Shearn A 
Published: January 2021

Abstract
The polycomb-group genes, a set of genes characterized by mutations that cause similar phenotypes and dosage-dependent interactions, are required for the normal expression of segment-specific homeotic loci. Here we report that polycombeotic (formerly 1(3)1902), originally identified by a lethal mutation that causes a small-disc phenotype, is also a member of this group of essential genes. Adults homozygous for temperature-sensitive pco alleles that were exposed to the restrictive temperature during larval life display the second and third leg to first leg transformation characteristic of polycomb-group mutants. Adult females homozygous for temperature-sensitive alleles exposed to the restrictive temperature during oogenesis produce embryos that show anterior segments with structures normally unique to the eighth abdominal segment, another transformation characteristic of polycomb-group mutants. Mutations in the polycombeotic gene also cause defects not reported for mutations in other polycomb-group genes. Females homozygous for the most extreme temperature-sensitive allele are sterile, and larvae homozygous for null alleles have small imaginal discs and reduced frequencies of mitotic figures in the brain. Dominant mutations originally identified as enhancers or suppressors of zeste are gain-of-function alleles of polycombeotic. The type and variety of defects displayed by different mutations in this gene indicate that the product might be involved in chromosome structure and/or function.
Mixed segregation of chromosomes during single-division meiosis of Saccharomyces cerevisiae.
Authors: Sharon G , Simchen G 
Published: January 2021

Abstract
Normal meiosis consists of two consecutive cell divisions in which all the chromosomes behave in a concerted manner. Yeast cells homozygous for the mutation cdc5, however, may be directed through a single meiotic division of a novel type. Dyad analysis of a cdc5/cdc5 strain with centromere-linked markers on four different chromosomes has shown that, in these meioses, some chromosomes within a given cell segregate reductionally whereas others segregate equationally. The choice between the two types of segregation in these meioses is made individually by each chromosome pair. Different chromosome pairs exhibit different segregation tendencies. Similar results were obtained for cells homozygous for cdc14.
Is there selection on RFLP differences in mitochondrial DNA?
Authors: Nigro L , Prout T 
Published: January 2021

Abstract
Experimental populations of Drosophila simulans were established for the purpose of detecting the presence or absence of selection on a restriction fragment length polymorphism in mitochondrial DNA (mtDNA). It was then discovered that the founding strains differed with respect to the Rickettsia-mediated incompatibility system in this species, which is maternally transmitted together with the mtDNA differences. A population model was constructed using the known fitness effects of the incompatibility system, with the result that the population trajectories can be completely explained by the effects of the microorganism with no need to invoke selection on mtDNA. The strong conclusion is that in this case we can rule out the strong selection proposed by MacRae and Anderson to explain the "dramatic mtDNA changes" in their Drosophila pseudoobscura populations. The population theory used for the experiments is discussed in the context of natural populations. Estimated parameters include the possibility that with two populations, one with the organism and one without it, there may be no bias as to which will invade the other, which in turn suggests no global tendency for the infection to spread or decline.
Mathematical models of gene amplification with applications to cellular drug resistance and tumorigenicity.
Authors: Kimmel M , Axelrod D E 
Published: January 2021

Abstract
An increased number of copies of specific genes may offer an advantage to cells when they grow in restrictive conditions such as in the presence of toxic drugs, or in a tumor. Three mathematical models of gene amplification and deamplification are proposed to describe the kinetics of unstable phenotypes of cells with amplified genes. The models differ in details but all assume probabilistic mechanisms of increase and decrease in gene copy number per cell (gene amplification/deamplification). Analysis of the models indicates that a stable distribution of numbers of copies of genes per cell, observed experimentally, exists only if the probability of deamplification exceeds the probability of amplification. The models are fitted to published data on the loss of methotrexate resistance in cultured cell lines, due to the loss of amplified dihydrofolate reductase gene. For two mouse cell lines unstably resistant to methotrexate the probabilities of amplification and deamplification of the dihydrofolate reductase gene on double minute chromosomes are estimated to be approximately 2% and 10%, respectively. These probabilities are much higher than widely presumed. The models explain the gradual disappearance of the resistant phenotype when selective pressure is withdrawn, by postulating that the rate of deamplification exceeds the rate of amplification. Thus it is not necessary to invoke a growth advantage of nonresistant cells which has been the standard explanation. For another analogous process, the loss of double minute chromosomes containing the myc oncogene from SEWA tumor cells, the growth advantage model does seem to be superior to the amplification and deamplification model. In a more theoretical section of the paper, it is demonstrated that gene amplification/deamplification can result in reduction to homozygosity, such as is observed in some tumors. Other applications are discussed.
Exchange of spacer regions between rRNA operons in Escherichia coli.
Authors: Harvey S , Hill C W 
Published: January 2021

Abstract
The Escherichia coli rRNA operons each have one of two types of spacer separating the 16S and 23S coding regions. The spacers of four operons encode tRNA(Glu2) and the other three encode both tRNA(Ile) and tRNA(Ala1B). We have prepared a series of mutants in which the spacer region of a particular rrn operon has been replaced by the opposite type. Included among these were a mutant retaining only a single copy of the tRNA(Glu2) spacer (at rrnG) and another retaining only a single copy of the tRNA(Ile)-tRNA(Ala1B) spacer (at rrnA). While both mutants grew more slowly than controls, the mutant deficient in tRNA(Glu2) spacers was more severely affected. At a frequency of 6 X 10(-5), these mutants phenotypically reverted to faster growing types by increasing the copy number of the deficient spacer. In most of these phenotypic revertants, the deficient spacer type appeared in a rrn operon which previously contained the surplus type, bringing the ratio of spacer types closer to normal. In a few cases, these spacer changes were accompanied by an inversion of the chromosomal material between the donor and recipient rrn operons. Two examples of inversion of one-half of the E. coli chromosome between rrnG and rrnH were observed. The correlation of spacer change with inversion indicated that, in these particular cases, the change was due to an intrachromatid gene conversion event accompanied by a reciprocal crossover rather than reciprocal exchange between sister chromatids.
Transposable element-induced response to artificial selection in Drosophila melanogaster: molecular analysis of selection lines.
Authors: Shrimpton A E , Mackay T F , Brown A J 
Published: January 2021

Abstract
Artificial selection lines for abdominal bristle score of Drosophila melanogaster established from P-M hybrid dysgenic crosses showed increases in selection response, heritability and phenotypic variance compared to similar lines started from nondysgenic crosses. To determine whether this increased genetic variance could be due to enhanced transposition of P elements following the dysgenic cross, the cytological locations (sites) of P elements were determined by in situ hybridization for the whole genome of samples of 20 individuals from the parental P strain, 20 individuals from each of the eight dysgenic selection lines, and ten individuals from each of the eight nondysgenic selection lines. Variation among and within the selection lines and the parental P strain in P element insertion sites was exceptionally high. A total of 601 sites were identified, but there was no difference in total number of sites per line, mean number of sites per individual, mean copy number per individual, or site frequency between dysgenic and nondysgenic selection lines, or between lines selected for high and low bristle score. Transposition following nondysgenic crosses may explain additional observations of accelerated selection responses in nondysgenic selection lines. It was not possible to deduce which, if any, of the several hundred insertions in the dysgenic selection lines were responsible for their extreme bristle phenotypes.
Genetic and molecular analysis of vgU and vgW: two dominant vg alleles associated with gene fusions in Drosophila.
Authors: Williams J A , Scott I M , Atkin A L , Brook W J , Russell M A , Bell J B 
Published: January 2021

Abstract
In the absence of a vg+ gene, extensive cell death occurs in third instar imaginal discs, which results in a complete loss of adult wing margin structures. Essentially all molecularly characterized vg alleles are associated with deletions or insertions of DNA into the vg locus. These alterations reduce or eliminate a 3.8-kb vg-specific transcript, resulting in recessive loss of function alleles. We report here the analysis of two dominant vg alleles which have been identified (vgU and vgW). The vgU allele is associated with a chromosomal inversion which splits the vg locus, resulting in a gene fusion between vg and the mastermind (mam) neurogenic locus. Reversion analysis of vgU indicates that sequences from the mam locus are required for vgU dominance. The vgW allele is also the result of a chromosomal inversion, in this case resulting in a gene fusion between vg and the homeobox-containing invected (inv) gene. It is also associated with novel dominant homeotic transformations. Revertant analysis indicates that sequences from inv are required for the dominant wing and dominant homeotic effects of vgW. The vg dominance does not appear to be mediated through a reduction of vg expression or a novel fusion transcript in either vgU or vgW. The results are consistent with a model in which inappropriate expression of inv causes the dominant homeotic effects seen in vgW.
Theoretical study of near neutrality. I. Heterozygosity and rate of mutant substitution.
Authors: Ohta T , Tachida H 
Published: January 2021

Abstract
In order to clarify the nature of "near neutrality" in molecular evolution and polymorphism, extensive simulation studies were performed. Selection coefficients of new mutations are assumed to be small so that both random genetic drift and selection contribute to determining the behavior of mutants. The model also incorporates normally distributed spatial fluctuation of selection coefficients. If the system starts from "average neutrality," it will move to a better adapted state, and most new mutations will become "slightly deleterious." Monte Carlo simulations have indicated that such adaptation is attained, but that the rate of such "progress" is very low for weak selection. In general, the larger the population size, the more effective the selection becomes. Also, as selection becomes weaker, the behavior of the mutants approaches that of completely neutral genes. Thus, the weaker the selection, the smaller is the effect of population size on mutant dynamics. Increase of heterozygosity with population size is very pronounced for subdivided populations. The significance of these results is discussed in relation to various observed facts on molecular evolution and polymorphism, such as generation-time dependency and overdispersion of the molecular clock, or contrasting patterns of DNA and protein polymorphism among some closely related species.
Mobility of two optional G + C-rich clusters of the var1 gene of yeast mitochondrial DNA.
Authors: Wenzlau J M , Perlman P S 
Published: January 2021

Abstract
Yeast mtDNA contains two different kinds of mobile optional sequences, two group I introns and a short G + C-rich insertion to some var1 genes. Movement of each element in crosses has been called gene conversion though little is known about the mechanism of G + C cluster conversion. A new allele of the var1 gene found in mtDNA of Saccharomyces capensis is described that permitted a more detailed comparison between intron mobility and G + C cluster conversion. The S. capensis var1 gene lacks the cc+ element present in all S. cerevisiae var 1 genes and the previously described optional a+ element. In crosses with cc+ a- and cc+ a+ S. cerevisiae strains, both clusters were found to be mobile and, in the latter cross, appear to convert independently and only to homologous insertion sites. No evidence for flanking marker coconversion (a hallmark feature of intron conversion) was obtained despite the availability of nearby physical markers on both sides of cluster conversion sites. These data indicate that G + C cluster conversion has only a superficial resemblance to intron mobility; analogies to procaryotic transposition mechanisms are considered.
Isolation and molecular characterization of the Aspergillus nidulans wA gene.
Authors: Mayorga M E , Timberlake W E 
Published: January 2021

Abstract
The walls of Aspergillus nidulans conidia contain a green pigment that protects the spores from damage by ultraviolet light. At least two genes, wA and yA, are required for pigment synthesis: yA mutants produce yellow spores, wA mutants produce white spores, and wA mutations are epistatic to yA mutations. We cloned wA by genetic complementation of the wA3 mutation with a cosmid library containing nuclear DNA inserts from the wild-type strain. The wA locus was mapped to an 8.5-10.5-kilobase region by gene disruption analysis. DNA fragments from this region hybridized to a 7500 nucleotide polyadenylated transcript that is absent from hyphae and mature conidia but accumulates during conidiation beginning when pigmented spores first appear. Mutations in the developmental regulatory loci brlA, abaA, wetA and apsA prevent wA mRNA accumulation. By contrast, yA mRNA fails to accumulate only in the brlA- and apsA- mutants. Thus, the level of wA transcript is regulated during conidiophore development and wA activation requires genes within the central pathway regulating conidiation.
Essential genes in the hDf6 region of chromosome I in Caenorhabditis elegans.
Authors: Howell A M , Rose A M 
Published: January 2021

Abstract
In this paper we describe the analysis of essential genes in the hDf6 region of chromosome I of Caenorhabditis elegans. Nineteen complementation groups have been identified which are required for the growth, survival or fertility of the organism (essential genes). Since ten of these genes were represented by more than one allele, a Poisson calculation predicts a minimum estimate of 25 essential genes in hDf6. The most mutable gene in this region was let-354 with seventeen alleles. An average mutation rate of 5 x 10(-5) mutations/gene/chromosome screened was calculated for an ethyl methanesulfonate dose of 15 mM. Mutations were recovered by screening for lethal mutations using the duplication sDp2 for recovery. Our analysis shows that duplications are very effective for maintenance and mapping of large numbers of lethal mutations. Approximately 600 lethal mutations were mapped in order to identify the 54 that are in the deficiency hDf6. The hDf6 region appears to have a lower proportion of early arresting mutations than other comparably sized regions of the genome.
Genetics of 51D-52A, a region containing several maternal-effect genes and two maternal-specific transcripts in Drosophila.
Authors: Underwood E M , Briot A S , Doll K Z , Ludwiczak R L , Otteson D C , Tower J , Vessey K B , Yu K 
Published: January 2021

Abstract
Two genomic clones exhibiting a maternal-specific pattern of expression map to cytological region 52A. To elucidate the function of these clones we have undertaken a mutagenesis of the cytological region 51D-52A. This paper presents the results of this screen and the preliminary analysis of female-sterile and lethal mutations isolated. A total of twelve complementation groups have been identified, four of which are defined exclusively by female-sterile alleles. Only one visible mutation was isolated, a recessive temperature-sensitive allele of Thickened-arista (Tarts). Several of the seven lethal loci display an embryonic lethal phase. Three of the four female-sterile loci affect chorion structure with one resulting in underamplification of the chorion genes, and two (possibly three) of the four female-steriles affect nuclear division/DNA replication. Thus it appears that this is a "developmentally important" region, possibly representing a clustering of genes involved in either DNA replication or nuclear division.