bluuebunny/crossref_metadata_2025_split huggingface dataset:
Interaction of the murine dilute suppressor gene (dsu) with fourteen coat color mutations.
Authors: Moore K J , Swing D A , Copeland N G , Jenkins N A 
Published: April 2021

Abstract
The murine dilute suppressor gene, dsu, was previously shown to suppress the dilute coat color phenotypes of mice homozygous for the dilute (d), leaden (ln), and ashen (ash) mutations. Each of these mutations produce adendritic melanocytes, which results in an abnormal transportation of pigment granules into the hair shaft and a diluted coat color. The suppression of each mutation is associated with the restoration of near normal melanocyte morphology, indicating that dsu can compensate for the absence of normal d, ln and ash gene products. In experiments described here, we have determined whether dsu can suppress the coat color phenotype of 14 additional mutations, at 11 loci, that affect coat color by mechanisms other than alterations in melanocyte morphology. In no case was dsu able to suppress the coat color phenotype of these 14 mutations. This suggests that dsu acts specifically on coat color mutations that result from an abnormal melanocyte morphology. Unexpectedly, dsu suppressed the ruby eye color of ruby-eye (ru) and ruby-eye-2 (ru-2) mice, to black. The exact nature of the defect producing these two mutant phenotypes is unknown. Histological examination of the pigmented tissues of the eyes of these mice indicated that dsu suppresses the eye color by increasing the overall level of pigmentation in the choroid but not the retinal pigmented epithelium. Choroid melanocytes, like those in the skin, are derived from the neural crest while melanocytes in the retinal pigmented epithelium are derived from the optic cup. This suggests that dsu may act specifically on neural crest-derived melanocytes. These studies have thus identified a second group of genes whose phenotypes are suppressed by dsu and have provided new insights into the mechanism of action of dsu.
Properties of a class of genes required for ray morphogenesis in Caenorhabditis elegans.
Authors: Baird S E , Emmons S W 
Published: April 2021

Abstract
We have identified eight mutations that define at least five terminal differentiation genes (ram genes) whose products are required during the extension of the male-specific ray sensilla in Caenorhabditis elegans. ram gene mutations result in morphological abnormalities in the sensory rays but do not appear to interfere with ray functions. A similar ray morphology phenotype was observed in males harboring mutations in three previously defined genes, dpy-11, dpy-18 and sqt-1, that also affect body shape. One of these genes, sqt-1, is known to encode a collagen. Mutations in different ram genes failed to complement, from which we infer that their gene products functionally interact. For one ram gene, failure to complement was shown to result from haploinsufficiency. Intergenic noncomplementation did not extend to the body morphology genes. The temperature-sensitive periods of both ram and body morphology mutations corresponded to the period of development in which ray extension occurs. We propose that ram gene products act together in a critical interaction between the rays and the cuticle required for wild-type ray morphology.
Genetic analysis of transvection effects involving cis-regulatory elements of the Drosophila Ultrabithorax gene.
Authors: Micol J L , Castelli-Gair J E , García-Bellido A 
Published: April 2021

Abstract
The Ultrabithorax (Ubx) gene of Drosophila melanogaster contains two functionally distinguishable regions: the protein-coding Ubx transcription unit and, upstream of it, the transcribed but nonprotein-coding bxd region. Numerous recessive, partial loss-of-function mutations which appear to be regulatory mutations map within the bxd region and within the introns of the Ubx transcription unit. In addition, mutations within the Ubx unit exons are known and most of these behave as null alleles. Ubx1 is one such allele. We have confirmed that, although the Ubx1 allele does not produce detectable Ubx proteins (UBX), it does retain other genetic functions detectable by their effects on the expression of a paired, homologous Ubx allele, i.e., by transvection. We have extended previous analyses made by E. B. Lewis by mapping the critical elements of the Ubx gene which participate in transvection effects. Our results show that the Ubx1 allele retains wild-type functions whose effectiveness can be reduced (1) by additional cis mutations in the bxd region or in introns of the Ubx transcription unit, as well as (2) by rearrangements disturbing pairing between homologous Ubx genes. Our results suggest that those remnant functions in Ubx1 are able to modulate the activity of the allele located in the homologous chromosome. We discuss the normal cis regulatory role of these functions involved in trans interactions between homologous Ubx genes, as well as the implications of our results for the current models on transvection.
copia expression is variable among natural populations of Drosophila.
Authors: Csink A K , McDonald J F 
Published: April 2021

Abstract
A survey of copia (retroviral-like element) expression in flies representing 37 populations worldwide of Drosophila melanogaster, Drosophila simulans and Drosophila mauritiana demonstrates that, although copia elements are present in all three species, copia-encoded transcripts are detectable only in D. melanogaster. Levels of copia transcripts vary nearly 100-fold among flies representing geographically diverse populations of D. melanogaster and this variation is not correlated with variability in copia copy number. Analysis of transcript levels in interpopulation hybrids demonstrates that much of this variability may be attributable to the action of trans-acting controls. The geographic and phylogenetic pattern of copia expression suggests that moderate to high levels of copia expression may be a relatively recent evolutionary acquisition. The potential evolutionary significance of these findings is discussed.
Characterization of the FB-NOF transposable element of Drosophila melanogaster.
Authors: Harden N , Ashburner M 
Published: April 2021

Abstract
FB-NOF is a composite transposable element of Drosophila melanogaster. It is composed of foldback sequences, of variable length, which flank a 4-kb NOF sequence with 308-bp inverted repeat termini. The NOF sequence could potentially code for a 120-kD polypeptide. The FB-NOF element is responsible for unstable mutations of the white gene (wc and wDZL) and is associated with the large TEs of G. Ising. Although most strains of D. melanogaster have 20-30 sites of FB insertion, FB-NOF elements are usually rare, many strains lack this composite element or have only one copy of it. A few strains, including wDZL and Basc have many (8-21) copies of FB-NOF, and these show a tendency to insert at "hot-spots." These strains also have an increased number of FB elements. The DNA sequence of the NOF region associated with TE146(Z) has been determined.
Evidence of extensive genetic exchange in the rp49 region among polymorphic chromosome inversions in Drosophila subobscura.
Authors: Rozas J , Aguadé M 
Published: April 2021

Abstract
Restriction map variation in 107 lines extracted from two natural populations of Drosophila subobscura was investigated with seven four-nucleotide-recognizing enzymes in a 1.6-kb region including the rp49 gene, that is located very close to the proximal breakpoint of inversion O3. Fourteen restriction site and 8 length polymorphisms, resulting in 73 haplotypes, have been identified. Estimated heterozygosity per nucleotide, pi = 0.0045, is comparable to the average nucleotide variation observed in Drosophila melanogaster. Because of the location of the rp49 region in D. subobscura, variation in three different gene arrangements-Ost, O3 + 4 and O3 + 4 + 8-has been compared. Out of 14 restriction site polymorphisms, 3 are shared by Ost, O3 + 4 and O3 + 4 + 8, and 3 additional ones are shared by Ost and O3 + 4, evidencing extensive genetic exchange among these polymorphic inversions. In agreement with previous data, the higher level of variation of O3 + 4 (as measured by haplotype diversity and nucleotide variation) suggests that O3 + 4 may be ancestral in relationship to extant gene arrangements.
The molecular basis of brown, an old mouse mutation, and of an induced revertant to wild type.
Authors: Zdarsky E , Favor J , Jackson I J 
Published: April 2021

Abstract
The murine b locus encodes the tyrosinase related protein, TRP-1, a putative membrane-bound, copper-containing enzyme having about 40% amino acid identity with tyrosinase. The protein is essential for production of black rather than brown hair pigment. We show that skin of mutant brown mice contains the same amount of TRP-1 mRNA as wild type. On sequencing the coding region of the mutant mRNA we find four nucleotide differences from the wild-type (Black) sequence. Two of these differences result in different amino acid residues encoded by the brown allele. By sequencing the TRP-1 gene from a mouse in which a reversion from brown to Black has been induced by ethylnitrosourea we are able to show that only one of these amino acid changes, which substitutes a tyrosine for a conserved cysteine, is the cause of the brown phenotype. This mutation is adjacent to another cysteine at which, in the analogous position in tyrosinase a mutation results in the albino phenotype. The sequence of the revertant is the first report of DNA sequence of an ethylnitrosourea-induced genetic change in mouse.
The expression of additive and nonadditive genetic variation under stress.
Authors: Blows M W , Sokolowski M B 
Published: April 2021

Abstract
Experimental lines of Drosophila melanogaster derived from a natural population, which had been isolated in the laboratory for approximately 70 generations, were crossed to determine if the expression of additive, dominance and epistatic genetic variation in development time and viability was associated with the environment. No association was found between the level of additive genetic effects and environmental value for either trait, but nonadditive genetic effects increased at both extremes of the environmental range for development time. The expression of high levels of dominance and epistatic genetic variation at environmental extremes may be a general expectation for some traits. The disruption of the epistatic gene complexes in the parental lines resulted in hybrid breakdown toward faster development and there was some indication of hybrid breakdown toward higher viability. A combination of genetic drift and natural selection had therefore resulted in different epistatic gene complexes being selected after approximately 70 generations from a common genetic base. After crossing, the hybrid populations were observed for 10 generations. Epistasis contributed on average 12 hr in development time. Fluctuating asymmetry in sternopleural bristle number also evolved in the hybrid populations, decreasing by &gt; 18% in the first seven generations after hybridization.
DNA synthesis errors associated with double-strand-break repair.
Authors: Strathern J N , Shafer B K , McGill C B 
Published: April 2021

Abstract
Repair of a site-specific double-strand DNA break (DSB) resulted in increased reversion frequency for a nearby allele. Site-specific DSBs were introduced into the genome of Saccharomyces cerevisiae by the endonuclease encoded by the HO gene. Expression of the HO gene from a galactose-inducible promoter allowed efficient DNA cleavage at a single site in large populations of cells. To determine whether the DNA synthesis associated with repair of DSBs has a higher error rate than that associated with genome duplication, HO-induced DSBs were generated 0.3 kb from revertible alleles of trp1. The reversion rate of the trp1 alleles was approximately 100-fold higher among cells that had experienced an HO cut than among uninduced cells. The reverted allele was found predominantly on the chromosome that experienced the DNA cleavage.
Host and phi X 174 mutations affecting the morphogenesis or stabilization of the 50S complex, a single-stranded DNA synthesizing intermediate.
Authors: Ekechukwu M C , Oberste D J , Fane B A 
Published: April 2021

Abstract
The morphogenetic pathway of bacteriophage phi X 174 was investigated in rep mutant hosts that specifically block stage III single-stranded DNA synthesis. The defects conferred by the mutant rep protein most likely affect the formation or stabilization of the 50S complex, a single-stranded DNA synthesizing intermediate, which consists of a viral prohead and a DNA replicating intermediate (preinitiation complex). phi X 174 mutants, ogr (rep), which restore the ability to propagate in the mutant rep hosts, were isolated. The org (rep) mutations confer amino acid substitutions in the viral coat protein, a constituent of the prohead, and the viral A protein, a constituent of the preinitiation complex. Four of the six coat protein substitutions are localized on or near the twofold axis of symmetry in the atomic structure of the mature virion.
Genetics of the synthesis of serine from glycine and the utilization of glycine as sole nitrogen source by Saccharomyces cerevisiae.
Authors: Sinclair D A , Dawes I W 
Published: April 2021

Abstract
Saccharomyces cerevisiae can grow on glycine as sole nitrogen source and can convert glycine to serine via the reaction catalyzed by the glycine decarboxylase multienzyme complex (GDC). Yeast strains with mutations in the single gene for lipoamide dehydrogenase (lpd1) lack GDC activity, as well as the other three 2-oxoacid dehydrogenases dependent on this enzyme. The LPD1 gene product is also required for cells to utilize glycine as sole nitrogen source. The effect of mutations in LPD1 (L-subunit of GDC), SER1 (synthesis of serine from 3-phosphoglycerate), ADE3 (cytoplasmic synthesis of one-carbon units for the serine synthesis from glycine), and all combinations of each has been determined. The results were used to devise methods for isolating mutants affected either in the generation of one-carbon units from glycine (via GDC) or subsequent steps in serine biosynthesis. The mutants fell into six complementation groups (gsd1-6 for defects in conversion of glycine to serine). Representatives from three complementation groups were also unable to grow on glycine as sole nitrogen source (gsd1-3). Assays of the rate of glycine uptake and decarboxylation have provided insights into the nature of the mutations.
Construction and analysis of yeast RNA polymerase II CTD deletion and substitution mutations.
Authors: West M L , Corden J L 
Published: April 2021

Abstract
The carboxyl-terminal domain (CTD) of the RNA polymerase II largest subunit plays an essential but poorly understood role in transcription. The CTD is highly phosphorylated in vivo and this modification may be important in the transition from transcription initiation to elongation. We report here the development of a strategy for creating novel yeast CTDs. We have used this approach to show that the minimum viable CTD in yeast contains eight consensus (Tyr1Ser2Pro3Thr4Ser5Pro6Ser7) heptapeptide repeats. Substitution of alanine or glutamate for serines in positions two or five is lethal. In addition, changing tyrosine in position one to phenylalanine is lethal. The effects of mutations that alter potential phosphorylation sites are consistent with a requirement for CTD phosphorylation in vivo.
The role of cdc2 and other genes in meiosis in Schizosaccharomyces pombe.
Authors: Iino Y , Hiramine Y , Yamamoto M 
Published: April 2021

Abstract
The requirement of the cdc2, cdc13 and cdc25 genes for meiosis in Schizosaccharomyces pombe was investigated using three different conditions to induce meiosis. These genes were known to be required for meiosis II. cdc13 and cdc25 are essential for meiosis I. The cdc2 gene, which is required for the initiation of both mitotic S-phase and M-phase, is essential for premeiotic DNA synthesis and meiosis II. The requirement of cdc2 for meiosis I was unclear. This contrasts with Saccharomyces cerevisiae, where CDC28, the homolog of cdc2, is required for meiosis I but not for premeiotic DNA synthesis. Expression of cdc13 and cdc25 was induced after premeiotic DNA synthesis, reaching a sharp peak before the first nuclear division. Expression of cdc22, encoding the large subunit of ribonucleotide reductase, was also induced but the peak was before premeiotic DNA synthesis. The induction of cdc13 and cdc25 was largely dependent on DNA synthesis and the function of the mei4 gene. The mei4 gene itself was also induced in a DNA synthesis-dependent manner. The chain of gene expression activating cdc25 may be important as part of the mechanism that ensures the dependency of nuclear division on DNA replication during meiosis.
Ribosomal RNA multigene loci: nomads of the Triticeae genomes.
Authors: Dubcovsky J , Dvorák J 
Published: April 2021

Abstract
The nucleolus organizing regions (NORs) on the short arms of chromosomes 1A(m) and 5A(m) of diploid wheat, Triticum monococcum L., are at the most distal loci in the linkage maps of these two chromosome arms. This distal location differs from the interstitial location of the Nor loci on chromosome arms 1BS of tetraploid Triticum turgidum L. and hexaploid T. aestivum L., 5DS of T. aestivum and diploid Ae. tauschii Coss., and 5HS of barley. Moreover, the barley 5HS locus is at a different location than the 5DS locus. However, other markers, including the centromeres, are colinear. These findings showed that the major Nor loci have repeatedly changed position in the chromosome arms during the radiation of species in the tribe Triticeae without rearrangements of the linkage groups. It is suggested that Nor loci may change position via dispersion of minor loci, that are shown here to exist in the T. monococcum genome, magnification of gene copy numbers in these minor loci, and subsequent deletion of the original major loci. Implications of these findings for the use of rRNA nucleotide sequences in phylogenetic reconstructions are pointed out.
Synonymous substitution rates in enterobacteria.
Authors: Eyre-Walker A , Bulmer M 
Published: April 2021

Abstract
It has been shown previously that the synonymous substitution rate between Escherichia coli and Salmonella typhimurium is lower in highly than in weakly expressed genes, and it has been suggested that this is due to stronger selection for translational efficiency in highly expressed genes as reflected in their greater codon usage bias. This hypothesis is tested here by comparing the substitution rate in codon families with different patterns of synonymous codon use. It is shown that the decline in the substitution rate across expression levels is as great for codon families that do not appear to be subject to selection for translational efficiency as for those that are. This implies that selection on translational efficiency is not responsible for the decline in the substitution rate across genes. It is argued that the most likely explanation for this decline is a decrease in the mutation rate. It is also shown that a simple evolutionary model in which synonymous codon use is determined by a balance between mutation, selection for an optimal codon, and genetic drift predicts that selection should have little effect on the substitution rate in the present case.
MUTATION-SELECTION BALANCE WITH STOCHASTIC SELECTION
Authors: Hartl Daniel L 
Published: April 2021

ABSTRACT
Diffusion theory has been used to analyze a model of mutation-selection balance in which the selection process is assumed to be stochastic in time. The limiting outcome of the mutation-stochastic selection process is determined qualitatively by the geometric mean fitnesses of the genotypes, and the conditions for fixation or polymorphism are similar to those that determine the outcome of the mutation-selection process when selection is constant. However, in the case of a completely recessive allele, detailed numerical study of the polymorphism associated with stochastic selection has shown that the average allele frequency maintained is greater than the equilibrium frequency expected when selection is constant, even when the geometric mean fitness of the recessive homozygotes is identical in the stochastic and deterministic models. Thus, allele frequencies in natural populations that are too high to be plausibly explained by a balance between mutation and constant selection can be accounted for if selection is stochastic.
RECOMBINATION PATHWAY SPECIFICITY OF CHI
Authors: Stahl Franklin W , Stahl Mary M 
Published: April 2021

ABSTRACT
Chi in phage λ is a genetic element increasing the rate of recombination in its vicinity. Chi activity requires the wild-type functions of both the recA and the recB genes of E. coli. In terms of the pathway concept for recombination, Chi is active in the RecBC pathway and inactive in the Red, RecE, and RecF pathways.
GENETICS OF YEAST HEXOKINASE
Authors: Lobo Zita , Maitra P K 
Published: April 2021

ABSTRACT
Two independent isolates of Saccharomyces cerevisiae lacking hexokinase activity (EC 2.7.1.1) are described. Both mutant strains grow on glucose but are unable to grow on fructose, and contain two mutant genes h×k1 and h×k2 each. The mutations are recessive and noncomplementing. Genetic analysis suggests that these two unlinked genes h×k1 and h×k2 determine, independently of each other, the synthesis of hexokinase isozymes P1 and P2, respectively. h×k1 is located on chromosome VIR distal to met10, and h×k2 is on chromosome IIIR distal to MAL2. Of four hexokinase-positive spontaneous reversions, one is very tightly linked to h×k1 and the other three to the h×k2 locus. The reverted enzymes are considerably more thermolabile than the respective wild-type enzymes, and in one case show altered immunological properties. Data are presented which suggest that the h×k1 and h×k2 mutations are missense mutations in the structural genes of hexokinase P1 and hexokinase P2, respectively. These are presumably the only enzymes that allow S. cerevisiae to grow on fructose.
A NEW GENE AFFECTING THE EFFICIENCY OF MATING-TYPE INTERCONVERSIONS IN HOMOTHALLIC STRAINS OF SACCHAROMYCES CEREVISIAE
Authors: Haber James E , Garvik Barbara 
Published: April 2021

ABSTRACT
Homothallic strains of Saccharomyes cerevisiae are able to switch efficiently from one mating genotype to another. From a single haploid spore arise both a and α mating type cells, which then self-mate to produce a colony consisting almost exclusively of nonmating a/α diploid cells. We have isolated a mutant homothallic strain that gives rise to colonies that show bisexual mating behavior. The mating reaction is always asymmetric, that is, in some colonies a mating is much stronger than α mating, while others show greater α than a mating.—This mating phenotype arises from the presence of three cell types in a colony: some a/α nonmating diploids and an unequal number of a and α haploid cells. The predominant haploid type is that of the original cell that gives rise to the colony. This mixture of cell types arises from a very reduced efficiency of homothallic mating-type interconversions in the mutant strain.—The mutation, designated switch (swi1-1), behaves as a single genetic locus. The mutation is centromere linked, but not linked to the mating type locus or to any of the homothallism genes: HO, HM a and HMα. The switch mutation does not affect the efficiency of self-mating, but rather directly affects the frequency of interconversion of mating types.