bluuebunny/crossref_metadata_2025 huggingface dataset:
Inference from clines stabilized by frequency-dependent selection.
Authors: Mallet J , Barton N
Published: January 2021

Frequency-dependent selection against rare forms can maintain clines. For weak selection, s, in simple linear models of frequency-dependence, single locus clines are stabilized with a maximum slope of between square root of s/square root of 8 sigma and square root of s/square root of 12 delta, where sigma is the dispersal distance. These clines are similar to those maintained by heterozygote disadvantage. Using computer simulations, the weak-selection analytical results are extended to higher selection pressures with up to three unlinked genes. Graphs are used to display the effect of selection, migration, dominance, and number of loci on cline widths, speeds of cline movements, two-way gametic correlations ("linkage disequilibria"), and heterozygote deficits. The effects of changing the order of reproduction, migration, and selection, are also briefly explored. Epistasis can also maintain tension zones. We show that epistatic selection is similar in its effects to frequency-dependent selection, except that the disequilibria produced in the zone will be higher for a given level of selection. If selection consists of a mixture of frequency-dependence and epistasis, as is likely in nature, the error made in estimating selection is usually less than twofold. From the graphs, selection and migration can be estimated using knowledge of the dominance and number of genes, of gene frequencies and of gametic correlations from a hybrid zone.
Genotypic variation for a quantitative character maintained under stabilizing selection without mutations: epistasis.
Authors: Gimelfarb A
Published: January 2021

A model of the gene action on a quantitative character is suggested. The model takes into account epistasis by combining multiplicative with the traditional additive approximation of the action of loci. It is demonstrated on the basis of this model that a high level of genotypic variation can be maintained in a population for a quantitative character under stabilizing selection in the absence of mutations, if there is epistasis. It is also shown that a large amount of additive variation as well as high heritability can be "hidden" in such a population and "released" if stabilizing selection is relaxed.
Antibiotic resistance mutations in the chloroplast 16S and 23S rRNA genes of Chlamydomonas reinhardtii: correlation of genetic and physical maps of the chloroplast genome.
Authors: Harris E H , Burkhart B D , Gillham N W , Boynton J E
Published: January 2021

Mutants resistant to streptomycin, spectinomycin, neamine/kanamycin and erythromycin define eight genetic loci in a linear linkage group corresponding to about 21 kb of the circular chloroplast genome of Chlamydomonas reinhardtii. With one exception, all of these mutants represent single base-pair changes in conserved regions of the genes encoding the 16S and 23S chloroplast ribosomal RNAs. Streptomycin resistance can result from changes at the bases equivalent to Escherichia coli 13, 523, and 912-915 in the 16S gene, or from mutations in the rps12 gene encoding chloroplast ribosomal protein S12. In the 912-915 region of the 16S gene, three mutations were identified that resulted in different levels of streptomycin resistance in vitro. Although the three regions of the 16S rRNA mutable to streptomycin resistance are widely separated in the primary sequence, studies by other laboratories of RNA secondary structure and protein cross-linking suggest that all three regions are involved in a common ribosomal neighborhood that interacts with ribosomal proteins S4, S5 and S12. Three different changes within a conserved region of the 16S gene, equivalent to E. coli bases 1191-1193, confer varying levels of spectinomycin resistance, while resistance to neamine and kanamycin results from mutations in the 16S gene at bases equivalent to E. coli 1408 and 1409. Five mutations in two genetically distinct erythromycin resistance loci map in the 23S rDNA of C. reinhardtii, at positions equivalent to E. coli 2057-2058 and 2611, corresponding to the rib3 and rib2 loci of yeast mitochondria respectively. Although all five mutants are highly resistant to erythromycin, they differ in levels of cross-resistance to lincomycin and clindamycin. The order and spacing of all these mutations in the physical map are entirely consistent with our genetic map of the same loci and thereby validate the zygote clone method of analysis used to generate this map. These results are discussed in comparison with other published maps of chloroplast genes based on analysis by different methods using many of the same mutants.
The genetics of the Dras3-Roughened-ecdysoneless chromosomal region (62B3-4 to 62D3-4) in Drosophila melanogaster: analysis of recessive lethal mutations.
Authors: Sliter T J , Henrich V C , Tucker R L , Gilbert L I
Published: January 2021

The genetic organization of interval 62B3-4 to 62D3-4 on the Drosophila third chromosome was investigated. The region (designated DRE) includes four known loci: Roughened (R; 3-1.4), defined by a dominant mutation disrupting eye morphology; the nonvital locus Aprt, structural gene for adenine phosphoribosyltransferase; Dras3, a homolog of the vertebrate ras oncogene; and 1(3)ecdysoneless (1(3)ecd), a gene that has been implicated in the regulation of larval molting hormone (ecdysteroid) synthesis. Overlapping chromosomal deletions of the region were generated by gamma-ray-induced reversion of the R mutation. Recessive lethal mutations were isolated based upon failure to complement the recessive lethality of Df(3L)RR2, a deletion of the DRE region that removes 16-18 polytene chromosome bands. A total of 117 mutations were isolated following ethyl methanesulfonate and gamma-ray mutagenesis. These and two additional define 13 lethal complementation groups. Mutations at two loci were recovered at disproportionately high rates. One of these loci is preferentially sensitive to radiation-induced mutational alterations. Additionally, an unusually low recovery rate for cytologically detectable rearrangement breakpoints within the gamma-ray-sensitive locus suggests that an interval of the DRE region closely linked to the R locus may be dominantly sensitive to position effects. Lethal phase analysis of mutant hemizygotes indicates that a high proportion of DRE-region loci (11 of 13) are necessary for larval development. Mutations in five loci cause predominantly first-instar larval lethality, while mutations in four other loci cause predominantly second-instar lethality. Mutations in two loci cause late-larval lethality associated with abnormal imaginal disc development. A temperature-sensitive allele of one newly identified complementation group blocks ecdysteroid-induced pupariation. This developmental block is overcome by dietary 20-hydroxyecdysone, suggesting that a second locus in the region in addition to l(3)ecd may play a role in the regulation of late larval ecdysteroid levels.
Statistical method for testing the neutral mutation hypothesis by DNA polymorphism.
Authors: Tajima F
Published: January 2021

The relationship between the two estimates of genetic variation at the DNA level, namely the number of segregating sites and the average number of nucleotide differences estimated from pairwise comparison, is investigated. It is found that the correlation between these two estimates is large when the sample size is small, and decreases slowly as the sample size increases. Using the relationship obtained, a statistical method for testing the neutral mutation hypothesis is developed. This method needs only the data of DNA polymorphism, namely the genetic variation within population at the DNA level. A simple method of computer simulation, that was used in order to obtain the distribution of a new statistic developed, is also presented. Applying this statistical method to the five regions of DNA sequences in Drosophila melanogaster, it is found that large insertion/deletion (greater than 100 bp) is deleterious. It is suggested that the natural selection against large insertion/deletion is so weak that a large amount of variation is maintained in a population.
Genetic analysis of temperature-sensitive lethal mutants of Salmonella typhimurium.
Authors: Schmid M B , Kapur N , Isaacson D R , Lindroos P , Sharpe C
Published: January 2021

We have isolated 440 mutants of Salmonella typhimurium that show temperature-sensitive growth on complex medium at 44 degrees. Approximately 16% of the mutations in these strains have been mapped to 17 chromosomal locations; two of these chromosomal locations seem to include several essential genes. Genetic analysis of the mutations suggests that the collection saturates the genes readily mutable to a ts lethal phenotype in S. typhimurium. Physiological characteristics of the ts lethal mutants were tested: 6% of the mutants can grow at high temperature under anaerobic conditions, 17% can grow when the medium includes 0.5 M KCl, and 9% of the mutants die after a 2-hr incubation at the nonpermissive temperature. Most ts lethal mutations in this collection probably affect genes required for growth at all temperatures (not merely during high temperature growth) since Tn10 insertions that cause a temperature-sensitive lethal phenotype are rare.
Intragenic and extragenic suppressors of mutations in the heptapeptide repeat domain of Saccharomyces cerevisiae RNA polymerase II.
Authors: Nonet M L , Young R A
Published: January 2021

The largest subunit of RNA polymerase II contains a repeated heptapeptide sequence at its carboxy terminus. Yeast mutants with certain partial deletions of the carboxy-terminal repeat (CTR) domain are temperature-sensitive, cold-sensitive and are inositol auxotrophs. Intragenic and extragenic suppressors of the cold-sensitive phenotype of CTR domain deletion mutants were isolated and studied to investigate the function of this domain. Two types of intragenic suppressing mutations suppress the temperature-sensitivity, cold-sensitivity and inositol auxotrophy of CTR domain deletion mutants. Most intragenic mutations enlarge the repeat domain by duplicating various portions of the repeat coding sequence. Other intragenic suppressing mutations are point mutations in a conserved segment of the large subunit. An extragenic suppressing mutation (SRB2-1) was isolated that strongly suppresses the conditional and auxotrophic phenotypes of CTR domain mutations. The SRB2 gene was isolated and mapped, and an SRB2 partial deletion mutation (srb2 delta 10) was constructed. The srb2 delta 10 mutants are temperature-sensitive, cold-sensitive and are inositol auxotrophs. These phenotypes are characteristic of mutations in genes encoding components of the transcription apparatus. We propose that the SRB2 gene encodes a factor that is involved in RNA synthesis and may interact with the CTR domain of the large subunit of RNA polymerase II.
The mitochondrial genome organization of a maize fertile cmsT revertant line is generated through recombination between two sets of repeats.
Authors: Fauron C M , Havlik M , Brettell R I
Published: January 2021

The mitochondrial genome (mtDNA) organization from a fertile revertant line (V3) derived from the maize cytoplasmic male sterile type T (cmsT) callus tissue culture has been determined. We report that the sequence complexity can be mapped on to a circular "master chromosome" of 705 kb which includes a duplication of 165 kb of DNA when compared to its male sterile progenitor. Associated with this event is also a 0.423-kb deletion, which removed the cmsT-associated urf13 gene. As found for the maize normal type (N) and cmsT mitochondrial genomes, the V3 master chromosome also exists as a multipartite structure generated by recombination through repeated sequences.
Genetic characterization of the Saccharomyces cerevisiae translational initiation suppressors sui1, sui2 and SUI3 and their effects on HIS4 expression.
Authors: Castilho-Valavicius B , Yoon H , Donahue T F
Published: January 2021

Saccharomyces cerevisiae strains containing mutations of the HIS4 translation initiation AUG codon were studied by reversion analysis in an attempt to identify components of the translation initiation complex that might participate in initiation site selection during the scanning process. The genetic characterization of these revertants identified three unlinked suppressor loci: SUI1, SUI2 and sui3, which when mutated restored the expression of the HIS4 allele despite the absence of the AUG initiator codon. Both sui1 and sui2 are recessive and cause temperature-sensitive growth on enriched medium. The temperature-sensitive phenotype and the ability to restore HIS4 expression associated with either sui1 or sui2 mutations cosegregate in crosses. SUI3 mutations are dominant and do not alter the thermal profile for growth. None of the mutations at the three loci suppresses known frameshift, missense or nonsense mutations. Each is capable of suppressing the nine different point mutations of the initiator codon at HIS4 or HIS4-lacZ as well as a two base change (ACC) and a three base deletion of the AUG codon, suggesting that the site of suppression resides outside the normal initiator region. sui1 and sui2 suppressor mutations were mapped to chromosomes XIV and X, respectively. Suppression by sui1, sui2 and SUI3 mutations results in 14-, 11- and 47-fold increases, respectively, relative to isogenic parent strains, in the expression of a HIS4 allele lacking the initiator AUG codon. Part of this increase in the HIS4 expression by sui2 and SUI3 can be attributed to increases of HIS4 mRNA levels, presumably mediated by perturbation of the general amino acid control system of yeast.
How does the cell count the number of ectopic copies of a gene in the premeiotic inactivation process acting in Ascobolus immersus?
Authors: Faugeron G , Rhounim L , Rossignol J L
Published: January 2021

Repeated genes, artificially introduced in Ascobolus immersus by integrative transformation, are frequently inactivated during the sexual phase. Inactivation is observed in about 50% of meioses if duplicated genes are at ectopic chromosomal locations, and in 90% of meioses if genes are tandemly repeated. Inactivation is associated with extensive methylation of the cytosine residues of the duplicated sequences and is induced in the still haploid nuclei of the dikaryotic cell which will undergo karyogamy and subsequent meiosis. Only repeated sequences become methylated. This raises the intriguing question of how the premeiotic inactivation machinery is informed that a nucleus contains multiple copies of a gene. By using in crosses recombinant strains of A. immersus in which either one, two or three genetically independent copies of the exogenous amdS gene from Aspergillus nidulans had been introduced, we could follow the premeiotic inactivation of each one of the ectopic amdS copies. This led us to propose that a prerequisite for inactivation is a premeiotic pairing of repeated sequences and that each copy can undergo successive cycles of pairing. In fact, once methylated, a copy can pair with a still unmethylated copy, so that an uneven number of copies can be subject to inactivation.
Actin genes in the Mediterranean fruit fly, Ceratitis capitata.
Authors: Haymer D S , Anleitner J E , He M , Thanaphum S , Saul S H , Ivy J , Houtchens K , Arcangeli L
Published: January 2021

We have undertaken the study of actin gene organization and expression in the genome of the Mediterranean fruit fly (medfly), Ceratitis capitata. Actin genes have been extensively characterized previously in a wide range of eukaryotic organisms, and they have valuable properties for comparative studies. These genes are typically highly conserved in coding regions, represented in multiple copies per genome and regulated in expression during development. We have isolated a gene in the medfly using the cloned Drosophila melanogaster 5C actin gene as a probe. This medfly gene detects abundant messages present during late larval and late pupal development as well as in thoracic and leg tissue preparations from newly emerged adults. This pattern of expression is consistent with what has been seen for actin genes in other organisms. Using either the D. melanogaster 5C actin gene or the medfly gene as a probe identifies five common cross reacting EcoRI fragments in genomic DNA, but only under less than fully stringent hybridization conditions.
Production of null mutants in the major intestinal esterase gene (ges-1) of the nematode Caenorhabditis elegans.
Authors: McGhee J D , Birchall J C , Chung M A , Cottrell D A , Edgar L G , Svendsen P C , Ferrari D C
Published: January 2021

The ges-1 gene of the nematode Caenorhabditis elegans codes for a nonspecific carboxylesterase that is expressed only in the intestinal lineage. This esterase has turned out to be a convenient biochemical marker for lineage-specific differentiation. In the present paper, we describe the production of several C. elegans strains that lack detectable activity of the ges-1 esterase. To isolate these ges-1 null strains, we first produced a strain of hermaphrodites in which the wild-type copy of the ges-1 gene was stably balanced over a previously isolated isoelectric focusing allele, ges-1(ca6); this parental strain was then mutagenized with EMS and isoelectric focusing gels were used to identify progeny populations that lacked either ges-1(+) or ges-1(ca6) esterase activity. This method is a straightforward and general approach to obtaining null mutations in any gene that has a biochemical or immunological assay. The ges-1 gene is not essential to worm survival, development or reproduction. Furthermore, lack of the ges-1 product has no obvious effect on the ability of worms (containing either normal or greatly reduced levels of acetylcholinesterases) to survive exposure to esterase inhibitors. The ges-1 gene product provides roughly half of the total esterase activity measured in crude extracts of L1 larvae or mixed worm populations. However, histochemical staining of individual ges-1(0) embryos shows that the ges-1 esterase is the first and essentially the only esterase to be produced during embryonic development, from the midproliferation phase up to at least the twofold stage of morphogenesis. These ges-1(0) strains now allow us to investigate the developmental control of the ges-1 gene by DNA-mediated transformation, in which the ges-1 gene acts as its own reporter.
The translational activator GCN3 functions downstream from GCN1 and GCN2 in the regulatory pathway that couples GCN4 expression to amino acid availability in Saccharomyces cerevisiae.
Authors: Hannig E M , Williams N P , Wek R C , Hinnebusch A G
Published: January 2021

The GCN4 protein of S. cerevisiae is a transcriptional activator of amino acid biosynthetic genes which are subject to general amino acid control. GCN3, a positive regulator required for increased GCN4 expression in amino acid-starved cells, is thought to function by antagonism of one or more negative regulators encoded by GCD genes. We isolated gcn3c alleles that lead to constitutively derepressed expression of GCN4 and amino acid biosynthetic genes under its control. These mutations map in the protein-coding sequences and, with only one exception, do not increase the steady-state level of GCN3 protein. All of the gcn3c alleles lead to derepression of genes under the general control in the absence of GCN1 and GCN2, two other positive regulators of GCN4 expression. This finding suggests that GCN3 functions downstream from GCN1 and GCN2 in the general control pathway. In accord with this idea, constitutively derepressing alleles of GCN2 are greatly dependent on GCN3 for their derepressed phenotype. The gcn3c alleles that are least dependent on GCN1 and GCN2 for derepression cause slow-growth under nonstarvation conditions. In addition, all of the gcn3c alleles are less effective than wild-type GCN3 in overcoming the temperature-sensitive lethality associated with certain mutations in the negative regulator GCD2. These results suggest that activation of GCN3 positive regulatory function by the gcn3c mutations involves constitutive antagonism of GCD2 function, leading to reduced growth rates and derepression of GCN4 expression in the absence of amino acid starvation.
A polymerization model of chiasma interference and corresponding computer simulation.
Authors: King J S , Mortimer R K
Published: January 2021

A model of chiasma interference is proposed and simulated on a computer. The model uses random events and a polymerization reaction to regulate meiotic recombination between and along chromosomes. A computer simulation of the model generates distributions of crossovers per chromosome arm, position of events along the chromosome arm, distance between crossovers in two-event tetrads, and coincidence as a function of distance. Outputs from the simulation are compared to data from Saccharomyces cerevisiae and the X chromosome of Drosophila melanogaster. The simulation demonstrates that the proposed model can produce the regulation of recombination observed in both genetic and cytological experiments. While the model was quantitatively compared to data from only Drosophila and Saccharomyces, the regulation observed in these species is qualitatively similar to the regulation of recombination observed in other organisms.
Random segregation of chromatids at mitosis in Saccharomyces cerevisiae.
Authors: Neff M W , Burke D J
Published: January 2021

Previous experiments suggest that mitotic chromosome segregation in some fungi is a nonrandom process in which chromatids of the same replicative age are destined for cosegregation. We have investigated the pattern of chromatid segregation in Saccharomyces cerevisiae by labeling the DNA of a strain auxotrophic for thymidine with 5-bromodeoxyuridine. The fate of DNA strands was followed qualitatively by immunofluorescence microscopy and quantitatively by microphotometry using an anti-5-bromodeoxyuridine monoclonal antibody. Chromatids of the same replicative age were distributed randomly to daughter cells at mitosis. Quantitative measurements showed that the amount of fluorescence in the daughter nuclei derived from parents with hemilabeled chromosomes diminished in intensity by one half. The concentration of 5-bromodeoxyuridine used in the experiments had little effect on the frequency of either homologous or sister chromatid exchanges. We infer that the 5-bromodeoxyuridine was distributed randomly due to mitotic segregation of chromatids and not via sister chromatid exchanges.
Photoregulation of the Cat2 and Cat3 catalase genes in pigmented and pigment-deficient maize: the circadian regulation of Cat3 is superimposed on its quasi-constitutive expression in maize leaves.
Authors: Acevedo A , Williamson J D , Scandalios J G
Published: January 2021

We have investigated the accumulation of Cat2 and Cat3 catalase transcripts in 6-7-day postimbibition leaves of normally pigmented and pigment-deficient maize seedlings under different light regimes. In seedlings of normal inbred maize lines Cat2 mRNA accumulates to significantly higher levels in either continuous light or a diurnal light/dark cycle than in continuous dark. In contrast to the high levels of the Cat2 message observed in their wild-type siblings, carotenoid-deficient mutants accumulate Cat2 mRNA at barely detectable levels. Mutants deficient in chlorophylls, but having normal carotenoid levels, accumulate normal levels of Cat2 mRNA. This suggests that both light and carotenoids are required for the normal accumulation of the Cat2 message. The steady-state level of Cat3 RNA exhibits a dramatic diurnal variation when seedlings are grown under a 24-hr light/dark cycle. We have previously shown that this variation is at the level of Cat3 gene transcription and is under the control of a novel circadian rhythm. In this study we show that both pigment-deficient mutants and their wild-type siblings exhibit the normal diurnal pattern of Cat3 RNA accumulation. This indicates that photosynthetic pigments, allelic variation, and genetic background do not directly affect the temporal pattern of Cat3 accumulation in leaves. We observed, however, that when normal plants are grown in either continuous light or continuous dark, the Cat3 transcript in leaves is present at uniformly high levels throughout the 24-hr sampling period.(ABSTRACT TRUNCATED AT 250 WORDS)
Directed synthesis of a segmental chromosomal transposition: an approach to the study of chromosomes lethal to the gametophyte generation of maize.
Authors: Birchler J A , Levin D M
Published: January 2021

Because of the haploid nature of the gametophyte generation of plants, most mutations that are lethal or detrimental to the gametophytes cannot be recovered. Our laboratory is currently developing several techniques to overcome this situation. In this paper, a procedure is described to generate directed segmental chromosomal transpositions. The method involves recovery of recombinants between reciprocal translocation overlaps such that one region of the genome is inserted into a nonhomologous chromosome in a predetermined and directed manner. This duplicated segment then could serve to cover deficiencies or mutations, lethal to the gametophytes, in the region from whence it originated. The manipulation of segmental chromosomal transpositions for analyzing mutants lethal or detrimental to the gametophyte generation is discussed. The procedure to generate transpositions, the translocations between normal A and supernumerary B chromosomes that generate deficiencies in the male gametes, the r-X1 chromosome that generates deficiencies in the female gametes and other techniques available in maize form a system to analyze gametophyte lethal mutations.
Mutant tryptophan aporepressors with altered specificities of corepressor recognition.
Authors: Arvidson D N , Shapiro M , Youderian P
Published: January 2021

The Escherichia coli trpR gene encodes tryptophan aporepressor, which binds the corepressor ligand, L-tryptophan, to form an active repressor complex. The side chain of residue valine 58 of Trp aporepressor sits at the bottom of the corepressor (L-tryptophan) binding pocket. Mutant trpR genes encoding changes of Val58 to the other 19 naturally occurring amino acids were made. Each of the mutant proteins requires a higher intracellular concentration of tryptophan for activation of DNA binding than wild-type aporepressor. Whereas wild-type aporepressor is activated better by 5-methyltryptophan (5-MT) than by tryptophan, Ile58 and other mutant aporepressors prefer tryptophan to 5-MT as corepressor, and Ala58 and Gly58 prefer 5-MT much more strongly than wild-type aporepressor in vivo. These mutant aporepressors are the first examples of DNA-binding proteins with altered specificities of cofactor recognition.
The response to artificial selection from new mutations in Drosophila melanogaster.
Authors: Caballero A , Toro M A , López-Fanjul C
Published: January 2021

Twenty generations of divergent selection for abdominal bristle number were carried out starting from a completely homozygous population of Drosophila melanogaster. All lines were selected with the same proportion (20%) but at two different numbers of selected parents of each sex (5 or 25). A significant response to selection was detected in eight lines (out of 40) and, in most cases, it could be wholly attributed to a single mutation of relatively large effect (0.5-2 phenotypic standard deviations). The ratio of new mutational variance to environmental variance was estimated to be (0.33 +/- 0.11) X 10(-3). The distribution of mutant effects was asymmetrical, both with respect to bristle number (85% of it was negative) and to fitness (most detected bristle mutations were lethal or semilethal). Moreover, this distribution was leptokurtic, due to the presence of major genes. Gene action on bristles ranged from additive to completely recessive, no epistatic interactions being found. In agreement with theory, larger responses in each direction were achieved by those lines selected at greater effective population sizes. Furthermore, the observed divergence between lines selected in opposite directions was proportional to their effective size, as predicted for mutations of large effect.
The mechanism of inducer formation in gal3 mutants of the yeast galactose system is independent of normal galactose metabolism and mitochondrial respiratory function.
Authors: Bhat P J , Hopper J E
Published: January 2021

Saccharomyces cerevisiae cells defective in GAL3 function exhibit either one of two phenotypes. The gal3 mutation in an otherwise normal cell causes a 2-5-day delay in the galactose triggered induction of GAL/MEL gene transcription. This long term adaptation (LTA) phenotype has been ascribed to inefficient inducer formation. The gal3 mutation causes a noninducible phenotype for GAL/MEL transcription if cells are defective in Leloir pathway function, in glycolysis or in respiratory function. It was recently shown that multiple copies of the intact GAL1 gene partially suppress the LTA phenotype of gal3 cells. Here we report that constitutively expressed GAL1 restored gal3 mutants to the rapidly inducible phenotype characteristic of wild-type cells and conferred rapid inducibility to gal3 gal10, gal3 gal7 or gal3 rho- strains that are normally noninducible. As shown by immunoblot analysis, the GAL1-mediated induction exhibits phosphorylation of the GAL4 protein, suggesting a mechanism similar to GAL3-mediated induction. Altogether our results indicate that the deciding factor in the inducibility of the GAL/MEL genes in gal3 strains is the Gal3p-like activity of Gal1p. Based on the above we conclude that inducer formation does not require normal metabolism of galactose nor does it require mitochondrial respiratory function. These conclusions vitiate previous explanations for gal3 associated long-term adaptation and noninducible phenotypes.
Introduction of the transposable element mariner into the germline of Drosophila melanogaster.
Authors: Garza D , Medhora M , Koga A , Hartl D L
Published: January 2021

A chimeric white gene (wpch) and other constructs containing the transposable element mariner from Drosophila mauritiana were introduced into the germline of Drosophila melanogaster using transformation mediated by the P element. In the absence of other mariner elements, the wpch allele is genetically stable in both germ cells and somatic cells, indicating that the peach element (i.e., the particular copy of mariner inserted in the wpch allele) is inactive. However, in the presence of the active element Mos1, the wpch allele reverts, owing to excision of the peach element, yielding eye-color mosaics and a high rate of germline reversion. In strains containing Mos1 virtually every fly is an eye-color mosaic, and the rate of wpch germline reversion ranges from 10 to 25%, depending on temperature. The overall rates of mariner excision and transposition are approximately sixfold greater than the rates in comparable strains of Drosophila simulans. The activity of the Mos1 element is markedly affected by position effects at the site of Mos1 insertion. In low level mosiac lines, dosage effects of Mos1 are apparent in the heavier level of eye-color mosaicism in Mos1 homozygotes than in heterozygotes. However, saturation occurs in high level mosaic lines, and then dosage effects are not observed. A pBluescribe M13+ plasmid containing Mos1 was injected into the pole plasm of D. melanogaster embryos, and the Mos1 element spontaneously integrated into the germline at high efficiency. These transformed strains of D. melanogaster presently contain numerous copies of mariner and may be useful in transposon tagging and other applications.
Analysis of coyote mitochondrial DNA genotype frequencies: estimation of the effective number of alleles.
Authors: Lehman N , Wayne R K
Published: January 2021

A restriction-site survey of 327 coyotes (Canis latrans) from most parts of their North American range reveals 32 mitochondrial DNA (mtDNA) genotypes. The genotypes are not strongly partitioned in space, suggesting that there is high gene flow among coyote subpopulations. Consequently, each new geographic location added to the study has a decreasing probability of containing a mtDNA genotype that had not been previously discovered. This being the case, by using Monte Carlo sampling experiments, we can estimate the total number of genotypes that would be found if all possible localities were surveyed. This estimate of total genotypic variability agrees qualitatively with estimates based on theoretical considerations of the expected number of alleles in a stable population. We also predict effective population sizes from genotype data. The accuracy of these estimates is thought to be dependent on the fact that coyotes are not highly genetically structured, a situation which may apply to highly mobile species.
Saccharomyces cerevisiae null mutants in glucose phosphorylation: metabolism and invertase expression.
Authors: Walsh R B , Clifton D , Horak J , Fraenkel D G
Published: January 2021

A congenic series of Saccharomyces cerevisiae strains has been constructed which carry, in all combinations, null mutations in the three genes for glucose phosphorylation: HXK1, HXK2 and GLK1, coding hexokinase 1 (also called PI or A), hexokinase 2 (PII or B), and glucokinase, respectively: i.e., eight strains, all of which grow on glucose except for the triple mutant. All or several of the strains were characterized in their steady state batch growth with 0.2% or 2% glucose, in aerobic as well as respiration-inhibited conditions, with respect to growth rate, yield, and ethanol formation. Glucose flux values were generally similar for different strains and conditions, provided they contained either hexokinase 1 or hexokinase 2. And their aerobic growth, as known for wild type, was largely fermentative with ca. 1.5 mol ethanol made per mol glucose used. The strain lacking both hexokinases and containing glucokinase was an exception in having reduced flux, a result fitting with its maximal rate of glucose phosphorylation in vitro. Aerobic growth of even the latter strain was largely fermentative (ca. 1 mol ethanol per mol glucose). Invertase expression was determined for a variety of media. All strains with HXK2 showed repression in growth on glucose and the others did not. Derepression in the wild-type strain occurred at ca. 1 mM glucose. The metabolic data do not support- or disprove-a model with HXK2 having only a secondary role in catabolite repression related to more rapid metabolism.
Influence of gene flow and breeding tactics on gene diversity within populations.
Authors: Chesser R K
Published: January 2021

Expressions describing the accumulation of gene correlations within and among lineages and individuals of a population are derived. The model permits different migration rates by males and females and accounts for various breeding tactics within lineages. The resultant equations enable calculation of the probabilistic quantities for the fixation indices, rates of loss of genetic variation, accumulation of inbreeding, and coefficients of relationship for the population at any generation. All fixation indices were found to attain asymptotic values rapidly despite the consistent loss of genetic variation and accumulation of inbreeding within the population. The time required to attain asymptotic values, however, was prolonged when gene flow among lineages was relatively low (less than 20%). The degree of genetic differentiation among breeding groups, inbreeding coefficients, and gene correlations within lineages were found to be primarily functions of breeding tactics within groups rather than gene flow among groups. Thus, the asymptotic value of S. Wright's island model is not appropriate for describing genetic differences among groups within populations. An alternative solution is provided that under limited conditions will reduce to the original island model. The evolution of polygynous breeding tactics appears to be more favorable for promoting intragroup gene correlations than modification of migration rates. Inbreeding and variance effective sizes are derived for populations that are structured by different migration and breeding tactics. Processes that reduce the inbreeding effective population size result in a concomitant increase in variance effective population size.
Seventeen complementation groups of mutations decreasing meiotic recombination in Schizosaccharomyces pombe.
Authors: De Veaux L C , Hoagland N A , Smith G R
Published: January 2021

We have analyzed 43 recessive mutations reducing meiotic intragenic recombination in Schizosaccharomyces pombe. These mutations were isolated by a screen for reduced plasmid-by-chromosome recombination at the ade6 locus. Sixteen of the mutations define 10 new complementation groups, bringing to 17 the number of genes identified to be involved in meiotic recombination. The mutations were grouped into three discrete classes depending on the severity of the recombination deficiency in crosses involving the ade6-M26 recombination hotspot. Class I mutations caused at least a 1000-fold reduction in M26-stimulated intragenic recombination at the ade6 locus. Class II mutations reduced M26-stimulated recombination approximately 100-fold. Class III mutations caused a 3-10-fold reduction in either M26-stimulated or non-hotspot recombination. We obtained multiple alleles of class I and class II mutations, suggesting that we may be nearing saturation for mutations of this type. As a first step toward mapping, we used mitotic segregation to assign fourteen of the rec genes to chromosomes. Mutations in the six rec genes tested also caused a decrease in intragenic recombination at the ura4 locus; five of these mutations also reduced intergenic recombination between the pro2 and arg3 genes. These results indicate that these multiple rec gene products are required for high level meiotic recombination throughout the S. pombe genome.
Synaptonemal complexes from DNase-treated rat pachytene chromosomes contain (GT)n and LINE/SINE sequences.
Authors: Pearlman R E , Tsao N , Moens P B
Published: January 2021

Purified chromosome cores (synaptonemal complexes) of rat pachytene chromosomes, from which the chromatin is removed by extensive DNase II digestion, retain a residual class of DNA, presumably the bases of chromatin loops. This synaptonemal complex-associated DNA, isolated by proteinase digestion and phenol extraction of purified DNase-treated synaptonemal complexes, and cloned in plasmid vector pEMBL18, has a length distribution of 50-500 bp. From a library of these fragments, 21 fragments were sequenced. Present in this sample are short 40-200-bp segments with greater than 80% identity to "long" and "short" interspersed repeated elements (LINE/SINEs), an excess of GT/CA tandem repeats and a number of unidentified sequences. The LINE/SINE segments may play a role in homology vs. nonhomology recognition during meiosis and the alternating purine-pyrimidine sequences have been implicated in genetic recombination. Their enrichment in synaptonemal complexes may be related to the synapsis and recombination functions of meiosis.
Turnover of R1 (type I) and R2 (type II) retrotransposable elements in the ribosomal DNA of Drosophila melanogaster.
Authors: Jakubczak J L , Zenni M K , Woodruff R C , Eickbush T H
Published: January 2021

R1 and R2 are distantly related non-long terminal repeat retrotransposable elements each of which inserts into a specific site in the 28S rRNA genes of most insects. We have analyzed aspects of R1 and R2 abundance and sequence variation in 27 geographical isolates of Drosophila melanogaster. The fraction of 28S rRNA genes containing these elements varied greatly between strains, 17-67% for R1 elements and 2-28% for R2 elements. The total percentage of the rDNA repeats inserted ranged from 32 to 77%. The fraction of the rDNA repeats that contained both of these elements suggested that R1 and R2 exhibit neither an inhibition of nor preference for insertion into a 28S gene already containing the other type of element. Based on the conservation of restriction sites in the elements of all strains, and sequence analysis of individual elements from three strains, nucleotide divergence is very low for R1 and R2 elements within or between strains (less than 0.6%). This sequence uniformity is the expected result of the forces of concerted evolution (unequal crossovers and gene conversion) which act on the rRNA genes themselves. Evidence for the role of retrotransposition in the turnover of R1 and R2 was obtained by using naturally occurring 5' length polymorphisms of the elements as markers for independent transposition events. The pattern of these different length 5' truncations of R1 and R2 was found to be diverse and unique to most strains analyzed. Because recombination can only, with time, amplify or eliminate those length variants already present, the diversity found in each strain suggests that retrotransposition has played a critical role in maintaining these elements in the rDNA repeats of D. melanogaster.
RFLPs for somatotropic genes identify quantitative trait loci for growth in mice.
Authors: Winkelman D C , Hodgetts R B
Published: January 2021

Restriction fragment length polymorphisms for somatotropic genes were tested for associations with body weight and postweaning growth rate in mice. Polymorphisms for growth hormone (GH) and insulin-like growth factor 2 (IGF-2) genes were identified in stock population lines which had been subjected to long-term selection for high 42-day body weight (H lines) or randomly mated (FP and C lines). Two F2 populations of mice (5F2 and MF2) were generated from crosses between a single H line of mice and two unselected control lines and subsequently, two divergently weight selected sublines were generated from each F2 population. The GHh allele which had originally been fixed in three of four H lines and absent from all FP and C lines was found to have a significant (P less than 0.01) effect on 42-day weight and postweaning growth rate in the F2 populations. However, GHh was associated with lower 42-day weight in the F2 populations, suggesting that the positive association between GHh and weight in the stock population was unique to the high weight selected genetic background of those lines. In agreement with this, the frequency of GHh increased in sublines selected for high 42-day weight and decreased in sublines selected for low 42-day weight. The IGF-2H5 allele was associated with higher weights in a sex-dependent manner in 5F2. In the high selected subline derived from 5F2, a significant increase in the frequency of IGF-2H5 was observed. Therefore this allele, in contrast to GHh, appears to be a positive indicator of growth irrespective of genetic background.
Nonrandom distribution of chloroplast recombination events in Chlamydomonas reinhardtii: evidence for a hotspot and an adjacent cold region.
Authors: Newman S M , Harris E H , Johnson A M , Boynton J E , Gillham N W
Published: January 2021

Intermolecular recombination of Chlamydomonas chloroplast genes has been analyzed in sexual crosses and following biolistic transformation. The pattern and position of specific exchange events within 15 kb of the 22-kb inverted repeat have been mapped with respect to known restriction fragment length polymorphism markers that distinguish the chloroplast genomes of the interfertile species Chlamydomonas reinhardtii and Chlamydomonas smithii. Recombinant progeny were selected from two- and three-factor crosses involving point mutations conferring herbicide (dr) and antibiotic resistance (er and spr) in the psbA, 23S and 16S ribosomal RNA genes, respectively. Exchange events were not randomly distributed over the 15-kb region, but were found to occur preferentially in a 0.7-kb sequence spanning the 3' end of the psbA gene and were much less common in an adjacent region of ca. 2.0 kb. These findings are corroborated by data showing that the dr mutation is unlinked genetically (3% recombination/kb) to the er and spr rRNA mutations, which are themselves linked and show ca. 1% recombination/kb. This discrepancy is significant since the dr-er and er-spr intervals are about the same length (ca. 7 kb). During chloroplast transformation, the 0.7-kb recombination hotspot also functions as a preferential site for exchange events leading to the integration of donor psbA gene sequences. The 0.7-kb hotspot region contains four classes of 18-37-bp direct repeats also found in other intergenic regions, but no open reading frame. Using deletion constructs in a chloroplast transformation assay, the hotspot was localized to a 500-bp region that lacks most of these repeats, which suggests that the repeats themselves are not responsible for the increased recombination frequency. Within this region, a 400-bp sequence is highly conserved between the chloroplast genomes of C. reinhardtii and C. smithii and includes several structural motifs characteristic of recombination hotspots in other systems.
Construction of a GAL1-regulated yeast cDNA expression library and its application to the identification of genes whose overexpression causes lethality in yeast.
Authors: Liu H , Krizek J , Bretscher A
Published: January 2021

We have constructed a galactose-inducible expression library by cloning yeast cDNAs unidirectionally under control of the GAL1 promoter in a centromeric shuttle vector. Eleven independent libraries were made each with an average size of about 1 x 10(6) clones, about 50 times larger than the reported mRNA population in a yeast cell. From this library, LEU2 and HIS3 cDNAs were recovered at a frequency of about 1 in 10(4) and in 12 out of 13 cases these were expressed in a galactose-dependent manner. Sequence analysis of leu2 and his3 complementing cDNAs indicates that they contain all the coding sequence and much of the 5' untranslated region. To test the utility of the library for the identification of genes whose overexpression confers a specific phenotype, we screened 25,000 yeast transformants for lethality on galactose. Among 15 clones that showed galactose inducible lethality were cDNAs encoding structural proteins, including ACT1 (actin), TUB2 (beta-tubulin) and ABP1 (actin-binding protein 1), and genes in signal transduction pathways, including TPK1 (a cAMP-dependent protein kinase) and GLC7 (type 1 protein phosphatase). cDNAs overexpressing NHPB (nonhistone protein B) and NSR1 (nuclear sequence recognition protein) were also found to be lethal. Among these, ACT1 was isolated four times, and NSR1 three times. The useful features of this library for cDNA cloning in yeast by complementation, and for the identification of genes whose over-expression confers specific phenotypes, are discussed.