bluuebunny/crossref_metadata_2025 huggingface dataset:
Temperature stabilization of a K110 variable energy cyclotron magnet
Authors: Kurashima Satoshi , Yuyama Takahiro , Okumura Susumu
Published: January 2021

For a large-scale cyclotron using normal conducting magnet coils, 10 h or more are required to obtain a highly stable magnetic field because heat transfer from the coils changes the temperature of the magnets gradually. To suppress the heat transfer and stabilize the magnet temperature in the TIARA K110 cyclotron, water-cooled copper plates were inserted between the main coil and the magnetic yoke. The heat generated by the main coil depends on its circulating current, which depends on the accelerated ion beam. To stabilize the magnet temperature, a technique was developed to control the temperature of the cooling water of the copper plates depending on the main coil current. Consequently, the temperature of the magnet was stabilized successfully to 24 ± 0.3 °C for various ion beams, and the magnetic field was maintained at ΔB/B = 1 × 10−5 after a few hours from initiating cyclotron operation.
A novel experimental apparatus for single polycrystalline diamond compact cutter tests
Authors: Dai Xianwei , Huang Zhongwei , Shi Huaizhong , Xiong Chao , Cheng Zhen
Published: January 2021

Polycrystalline diamond compact (PDC) bits are increasingly favored in the drilling field due to their high efficiency in rock breaking together with their longevity. To investigate the rock failure mechanism and further improve the performance of PDC bits, innovative experimental equipment is proposed in this paper. With its assistance, we can study the characteristics of rock-breaking using a PDC cutter under different conditions, e.g., high pressure and high temperature (HPHT), confining pressure, and jet impingement. The setup can be grouped into three parts: a rock cutting system, high-pressure jet generation system, and controlling system. A series of experiments was conducted to demonstrate the reliability of the setup. The results demonstrate the improvement in performance of PDC bits in the exploration of HPHT formations.
Transient thermocapillary convection flows in a rectangular cavity with an evenly heated lateral wall
Authors: Chen Enhui , Xu Feng
Published: January 2021

Transient thermocapillary convection flows driven by the evenly heated lateral wall of a rectangular cavity for zero-gravity condition are investigated by scaling analysis and numerical simulation. Scaling analysis suggests a set of flow regimes in different dynamical evolutions of the surface flow, dependent on Marangoni and Prandtl numbers and aspect ratios. In the typical case, the surface flow may travel, for example, under flow regimes of unsteady inertial-thermocapillary balance, unsteady viscous-thermocapillary balance, and steady viscous-thermocapillary balance in different dynamical evolutions. Additionally, scaling laws of the thickness and velocity of transient thermocapillary convection flows under different flow regimes have been obtained. Furthermore, two-dimensional numerical simulation has been performed. The numerical results show good agreement with the corresponding scaling predictions.
Carbon nanotubes in high-performance perovskite photovoltaics and other emerging optoelectronic applications
Authors: Habisreutinger Severin N. , Blackburn Jeffrey L.
Published: January 2021

In this perspective, we take a look back at the successful integration of carbon nanotubes (CNT) into high-efficiency solar cells based on metal-halide perovskites (MHPs). In addition to these successes, we identify critical questions and issues that remain to be addressed for the functionality of CNTs in MHP-based solar cells. Finally, we look forward toward potential future opportunities for CNT/MHP interfaces, in both new types of photovoltaic devices and other emerging optoelectronic applications.
Pilot hydrogen enhanced combustion in an ethylene-fueled scramjet combustor at Mach 4
Authors: Tian Ye , Shi Wen , Zhong Fuyu , Le Jialing
Published: January 2021

This paper describes a numerical and experimental investigation of the combustion process in an ethylene-fueled scramjet combustor. The combustion process could be divided into six parts. Part 1 consists of a nonreacting flow before the hydrogen was injected. In part 2, hydrogen injection led to the generation of a shock wave, resulting in an increase in the monitor pressure. Part 3 involved hydrogen combustion, including ignition and flame stabilization. The ignition time of the pilot hydrogen was about 26 ms, and the shock train generated by hydrogen combustion moved at about 20 m/s. In part 4, with the injection of ethylene, there was a hydrogen and ethylene combustion flow, the combustion became more intense, and the shock waves were pushed into the isolator and disappeared from the schlieren images. In part 5, with the cessation of hydrogen injection, the combustion involved ethylene alone, and the ethylene flame moved from the front of the cavity to the back. The combustion mode changed from subsonic to supersonic, and the flame stabilization mode changed from cavity recirculation to cavity shear layer combustion. In part 6, the flame was blown out and combustion ceased.
Comparison of measured and simulated spin-wave mode spectra of magnetic nanostructures
Authors: Nembach H. T. , McMichael R. D. , Schneider M. L. , Shaw J. M. , Silva T. J.
Published: January 2021

Motivated by the importance of magnetization dynamics in nanomagnets for the development and optimization of magnetic devices and sensors, we measured and modeled spin wave spectra in patterned elliptical nanomagnets. Ferromagnetic resonance spectra for multiple nanomagnets of Ni80Fe20, fabricated by electron-beam lithography to have nominal short-axes of 200 nm or 100 nm, were measured by use of heterodyne magneto-optical microwave microscopy. Scanning electron microscope images taken of the same nanomagnets were used to define element shapes for micromagnetic simulations. The measured spectra show significant differences between nominally identical nanomagnets, which could be only partially attributed to uncontrolled shape variations in the patterning process, as evidenced by the limited agreement between the measured and simulated spectra. Agreement between measurements and simulations was improved by including a zone of reduced magnetization and exchange at the edges of the nanomagnets in the simulations. Our results show that the reduction of shape variations between individual magnetic random-access memory elements can potentially improve their performance. However, unambiguous determination of materials parameters in nanomagnets based on analysis and modeling of spin wave spectra remains problematic.
Degree of Creeping Fat Assessed by Computed Tomography Enterography is Associated with Intestinal Fibrotic Stricture in Patients with Crohn’s Disease: A Potentially Novel Mesenteric Creeping Fat Index
Authors: Li Xue-Hua , Feng Shi-Ting , Cao Qing-Hua , Coffey J Calvin , Baker Mark E , Huang Li , Fang Zhuang-Nian , Qiu Yun , Lu Bao-Lan , Chen Zhi-Hui , Li Yi , Bettenworth Dominik , Iacucci Marietta , Sun Can-Hui , Ghosh Subrata , Rieder Florian , Chen Min-Hu , Li Zi-Ping , Mao Ren
Published: January 2021

Background and Aims

Emerging evidence points to a link between creeping fat and the pathogenesis of Crohn’s disease [CD]. Non-invasive assessment of the severity of creeping fat on cross-sectional imaging modality has seldom been investigated. This study aimed to develop and characterize a novel mesenteric creeping fat index [MCFI] based on computed tomography [CT] in CD patients.

Methods

MCFI was developed based on vascular findings on CT in a retrospective cohort [n = 91] and validated in a prospective cohort [n = 30]. The severity of creeping fat was graded based on the extent to which mesenteric fat extended around the intestinal circumference using the vessels in the fat as a marker. The accuracy of MCFI was assessed by comparing it with the degree of creeping fat observed in surgical specimens. The relationship between MCFI and fibrostenosis was characterized by determining if these correlated. The accuracy of MCFI was compared with other radiographic indices [i.e. visceral to subcutaneous fat area ratio and fibrofatty proliferation score].

Results

In the retrospective cohort, MCFI had moderate accuracy in differentiating moderate–severe from mild fibrostenosis (area under the receiver operating characteristic [ROC] curve [AUC] = 0.799; p = 0.000). ROC analysis in the retrospective cohort identified a threshold MCFI of > 3 which accurately differentiated fibrostenosis severity in the prospective cohort [AUC = 0.756; p = 0.018]. An excellent correlation was shown between MCFI and the extent of fat wrapping in specimens in the prospective cohort [r = 0.840, p = 0.000]. Neither visceral to subcutaneous fat area ratio nor fibrofatty proliferation score correlated well with the degree of intestinal fibrosis.

Conclusions

MCFI can accurately characterize the extent of mesenteric fat wrapping in surgical specimens. It may become another non-invasive measure of CD fibrostenosis.
A TEST OF SPATIAL AUTOCORRELATION ANALYSIS USING AN ISOLATION-BY-DISTANCE MODEL
Authors: Sokal Robert R , Wartenberg Daniel E
Published: January 2021

Using the isolation-by-distance model as an example, we have examined several assumptions of spatial autocorrelation analysis applied to gene frequency surfaces. Gene frequency surfaces generated by a simulation of Wright's isolation-by-distance model were shown to exhibit spatial autocorrelation, except in the panmictic case. Identical stochastic generating processes result in surfaces with characteristics that are functions of the process parameters, such as parental vagility and neighborhood size. Differences in these parameters are detectable as differences in spatial autocorrelations after only a few generations of the simulations. Separate realizations of processes with identical parameters yield similar spatial correlograms. We have examined the inferences about population structure that could have been made from these observations if they had been real, rather than simulated, populations. From such inferences, we could have drawn conclusions about the presence of selection, migration and drift in given natural systems.
A GENETIC ANALYSIS OF THE PTERIDINE BIOSYNTHETIC ENZYME, GUANOSINE TRIPHOSPHATE CYCLOHYDROLASE, IN DROSOPHILA MELANOGASTER
Authors: Mackay William J , O'Donnell Janis M
Published: January 2021

Strains with mutant eye color were surveyed for levels of GTP cyclohydrolase (GTP CH), the first enzyme acting in the biosynthesis of pteridines, the pigments causing red eye color in Drosophila. Six strains were found to have reduced GTP CH activity. In five of the six strains, the reduction of activity is apparent only in the adult head of homozygous mutants. We show that mutations in Punch (2-97, Pu) have severe effects on GTP CH activity. In most cases, the reduction of activity is apparent in all tissues and stages that express the enzyme. The activity of GTP CH is shown to be closely correlated with the number of Pu  + genes in the genome. One ethyl methanesulfonate (EMS)-induced Pu mutant has a GTP CH enzyme that is unstable when compared with the wild-type enzyme. Mutations in Pu fall into three general classes. The largest class has a recessive lethal and eye color phenotype, 50% or higher GTP CH activity in heterozygotes, and equivalent defects in all tissues. A second class is dominant in eye color phenotype and recessive lethal, with less than 50% GTP CH activity in heterozygotes. The third class is homozygous viable and has severe reduction of activity in the adult head, but no or less severe loss in other tissues.
NONIDEAL STATISTICS AND POSITIVE CORRELATION IN PHAGE RECOMBINATION: STUDIES WITH Λ TANDEM DUPLICATION PHAGES
Authors: Hays John B , Wolf Julie B , Zagursky Robert J
Published: January 2021

he question of nonideality in phage recombination, that is, the extent to which recombinant frequencies differ from those expected from the proportions of the two parental types in the mass culture, was addressed by experiments with λ tandem duplication phages. Isolation and genotypic analysis of triplication-phage progeny, all of which must be the result of intermolecular recombination, yielded a value of about 0.5 for the nonideality parameter h, i.e., the frequency of unlike-parent matings was only about ½ the "ideal" value. This value was independent of multiplicity and about the same for the Rec or Red recombination systems. Similar analysis of single-copy phage progeny yielded estimates of k, the ratio of intramolecular to intermolecular recombination of about ⅙ for the Rec system; no intramolecular events were detected in Red-mediated crosses. Consideration of known nonideality factors (finite input, limited number of intracellular sites for phage growth) suggests that the observed h values correspond to intracellular mixing efficiencies of 55 to 100%, depending on the number of intracellular phage growth sites assumed. Analysis of long-range positive correlation (negative interference) indicates that statistical effects caused unlike-parent double crossovers to be three to four times as frequent as an independent-event calculation would predict. In addition, Rec-mediated crosses showed a 1.3-fold positive correlation for unlike-parent crossovers (in a second interval) among the progeny of like-parent recombinations.
SPONTANEOUS MUTATIONS MODIFYING THE ACTIVITY OF ALCOHOL DEHYDROGENASE (ADH) IN DROSOPHILA MELANOGASTER
Authors: Mukai Terumi , Harada Ko , Yoshimaru Hiroshi
Published: January 2021

In a marked-inversion balanced lethal system of the second chromosome of Drosophila melanogaster, mutations were accumulated under minimum pressure of natural selection in 1000 individual lines that originated essentially from two individuals. After about 300 generations, the specific activities of alcohol dehydrogenase of 69 randomly selected individual lines were measured with replications using four replicated vials (on 2 days—two replications per day) by observing the reduction of NAD+ to NADH at 340 nm. Total soluble protein as the basis of standardization of enzyme activity was measured by the Lowry method for each vial. A control experiment was made immediately after the establishment of 20 individual lines from a single genotype. A significant increase in genetic variance was observed among the mutation-accumulating lines but was not detected in the control experiment. The statistical analysis of the data on the basis of the one-band/one-gene hypothesis suggests that many mutations controlling the activity of alcohol dehydrogenase occurred in regions different from the alcohol dehydrogenase locus itself, mainly in the noncoding DNA. Furthermore, it is suggested that transposon-like elements are related to the induction of these changes in alcohol dehydrogenase specific activities. Additional experimental evidence supporting this conclusion is also given.
SOME MODELS OF GENE CONVERSION FOR TREATING THE EVOLUTION OF MULTIGENE FAMILIES
Authors: Ohta Tomoko
Published: January 2021

A simple model of gene conversion presented earlier has been compared with a more general model under the assumption of no bias. The former is based on a simple concept that, by conversion, a gene (or a segment of a gene) is transferred from one locus to another in a multigene family. Intrachromatid symmetric conversion may result in reciprocal exchange of genes within a multigene family, and the previous theory of identity coefficients needs modification when it occurs. The relationship of various parameters of the two models was made clear in formulating the transition equations of identity coefficients. As an example of extending the analyses, a model of preferential conversion that is relevant to the observed uneven polymorphisms of class I genes in the major histocompatibility complex has been investigated. It differs from the biased conversion, in that directional process is through location of genes on the chromosome. It is shown that the model satisfactorily explains the observed data, even though the effect of preferential conversion is difficult to distinguish from that of natural selection.
ISOLATION AND CHARACTERIZATION OF NEUROSPORA MUTANTS AFFECTED IN INVERTASE SYNTHESIS
Authors: Lee Deborah B , Free Stephen J
Published: January 2021

We have outlined a procedure that allows the large-scale screening of mutagenized Neurospora crassa populations for invertaseless mutants. We have isolated and characterized three mutations, inv(DBL1), inv(DBL9) and inv(DBL14), which have been mapped at or near the invertase structural gene. One of these, inv(DBL1), is particularly interesting. Our experiments indicate that the reduced level of invertase activity in the inv(DBL1)-containing cell can be explained as the result of a reduced number of normal enzyme molecules. We also show that wild-type Neurospora is able to respond rapidly to a change of medium and can dramatically increase its production of invertase within 20 min after a transfer to a carbon-free medium.
MOLECULAR MAPPING OF A GENE CLUSTER FLANKING THE DROSOPHILA DOPA DECARBOXYLASE GENE
Authors: Gilbert Denise , Hirsh Jay , Wright T R F
Published: January 2021

Nine lethal complementation groups flanking the Drosophila Dopa decarboxylase (Ddc) gene, have been localized within 100 kb of cloned chromosomal DNA. Six of these complementation groups are within 23 kb of DNA, and all ten complementation groups, including Ddc, lie within 78-82 kb of DNA. The potential significance of this unusually high gene density is discussed.
A TEST FOR RARE MALE MATING ADVANTAGE WITH DROSOPHILA PSEUDOOBSCURA KARYOTYPES
Authors: Anderson Wyatt W , Brown Celeste J
Published: January 2021

Recent work has called into question the reality of the rare male mating advantage, pointing out that it could be a statistical artifact of marking flies for behavioral observation or of experimental bias in collecting males. We designed an experiment to test for rare male mating advantage that avoids these sources of bias. Large numbers of males of three Drosophila pseudoobscura karyotypes were allowed to mate with females of one karyotype in population cages. The females were then isolated before multiple mating occurred and their progeny used to diagnose the males that mated them. Populations were studied at five sets of male karyotypic frequencies. The mating success of the male homokaryotypes ST/ST and CH/CH, relative to that of the heterokaryotype ST/CH, was frequency dependent. Both ST/ST and CH/CH males displayed a statistically significant mating advantage at low frequency by comparision with their mating success in the midrange of karyotypic frequencies. Both male homokaryotypes also showed a significantly greater mating success at high homokaryotypic frequency than at intermediate frequencies, which is the same as saying that the heterokaryotype not only failed to show a rare male advantage but actually suffered a mating disadvantage at low frequency. We conclude that rare male mating advantage is not always an experimental or methodological artifact but does occur in laboratory populations of D. pseudoobscura. It may occur for some genotypes and not for others, however, and it may be only one of several forms of frequency-dependent mating behavior operating in a population.
IDENTIFICATION AND CHARACTERIZATION OF THE alc GENE PRODUCT OF BACTERIOPHAGE T4
Authors: Kutter Elizabeth , Drivdahl Rolf , Rand Keith
Published: January 2021

Bacteriophage T4 infection rapidly and almost completely inhibits transcription of host and other phage DNAs. Two processes have been implicated to date in this inhibition: (1) ADP ribosylation of the α subunits of the RNA polymerase, involving gp alt (which is injected with the phage DNA) and, later, gp mod; and (2) the action of the T4 alc/unf gene product, synthesized immediately after infection. The latter unfolds the host genome and also blocks transcription of cytosine-containing DNA. Here, we describe the identification on two-dimensional polyacrylamide gels of gp alc/unf, the more precise mapping of the gene and the identification and analysis of the appropriate DNA sequence from an Unf+  alc mutant.
THE GENETIC STRUCTURE OF NATURAL POPULATIONS OF DROSOPHILA MELANOGASTER. XVII. A POPULATION CARRYING GENETIC VARIABILITY EXPLICABLE BY THE CLASSICAL HYPOTHESIS
Authors: Kusakabe Shinichi , Mukai Terumi
Published: January 2021

About 400 second chromosomes were extracted from the Aomori population, a northernmost population of D. melanogaster on Honshu in Japan, and the following experimental results were obtained. (1) The frequency of lethal chromosomes was 0.23. (2) The effective size of the population was estimated to be about 3000, from the allelism rate of lethal chromosomes and their frequency. (3) The detrimental and lethal loads for viability were 0.243 and 0.242, respectively, and the D/L ratio became 1.00. (4) The average degree of dominance for mildly deleterious genes was estimated to be 0.178 ± 0.056. (5) Additive (α2  A) and dominance (α2  D) variances of viability were estimated to be 0.00276 ± 0.00090 and 0.00011 ± 0.00014, respectively. (6) There was no significant difference in environmental variances between homozygotes and heterozygotes. Using these estimates, we discuss the maintenance mechanisms of genetic variability of viability in the population. The mutation-selection balance explained these experimental results.
POPULATION BOTTLENECKS AND NONEQUILIBRIUM MODELS IN POPULATION GENETICS. I. ALLELE NUMBERS WHEN POPULATIONS EVOLVE FROM ZERO VARIABILITY
Authors: Maruyama Takeo , Fuerst Paul A
Published: January 2021

A simple numerical method was developed for the mean number and average age of alleles in a population that was initiated with no genetic variation following a sudden population expansion. The methods are used to examine the question of whether allele numbers are elevated compared with values seen in equilibrium populations having equivalent gene diversity. Excess allele numbers in expanding populations were found to be the rule. This was true whether the population began with zero variation or with low levels of variation in either of two initial distributions (initially an equilibrium allele frequency distribution or initially with loci occurring in only two classes of variation). Although the increase of alleles may persist for only a short time, when compared with the time which is required for approach to final equilibrium, the increase may be long when measured in absolute generation numbers. The pattern of increase in very rare alleles (those present only once in a sample) and the persistence of the original allele were also investigated.
COUPLING WITH PACKAGING EXPLAINS APPARENT NONRECIPROCALITY OF CHI-STIMULATED RECOMBINATION OF BACTERIOPHAGE LAMBDA BY RECA AND RECBC FUNCTIONS
Authors: Kobayashi Ichizo , Stahl Mary M , Fairfield Frederic R , Stahl Franklin W
Published: January 2021

Chi (Χ, 5'-GCTGGTGG) is a recombinator in RecA- and RecBC-mediated recombination in Escherichia coli. In vegetative recombination between two bacteriophage lambda strains, one with and the other without Chi (a  +Χ+  b  - × a-Χob+), the Χ-containing recombinant (a  -Χ+  b  -) is less abundant than the non-Χ-containing recombinant (a+Χob+). Previously this was taken was evidence for nonreciprocality of Χ-stimulated exchange. This inequality, however, is now seen to result from an event at cos (λ's packaging origin) that both activates Chi and initiates DNA packaging. An event at rightward cos leads to activation of leftward Χ on the same chromosome for an exchange to its left. From the resulting circulating dimer (-cos-a+-Χo-b+-cos-a--Χ+-b—), the cos that activated Χ is more likely to be used for rightward packaging initiation than is the cos from the other parent. Consistent with this coupling model is "biased packaging" in λ carrying two cos sites per monomer genome. When their maturation is dependent on dimerization by Χ-stimulated exchange, the phage particles result more often from packaging from the cos that activates Χ than from packaging from the other cos. Since Chi activation and packaging can be uncoupled, we infer that some early and reversible step in packaging activates Χ. A strong candidate for this step is a double-strand break at cos that provides an oriented entry site for a recombinase.
ISOLATION AND GENETIC ANALYSIS OF CAULOBACTER MUTANTS DEFECTIVE IN CELL SHAPE AND MEMBRANE LIPID SYNTHESIS
Authors: Hodgson David A , Shaw Penny , Shapiro Lucille
Published: January 2021

In this paper we report the isolation, characterization and genetic analysis of several C. crescentus mutants altered in membrane lipid synthesis. One of these, a fatty acid bradytroph, AE6002, was shown to be due to a mutation in the fatA gene. In addition to the presence of the fatA506 mutation, this strain was found to contain two other mutations, one of which caused the production of a water-soluble brown-orange pigment (pigA) and another which caused formation of helical cells (hclA). Expression of the latter two phenotypes required complex media and both were repressed by glucose. However, the lesions were mapped to loci that are separated by a substantial distance. The hclA and the fatA genes mapped close together, possibly implying that comutation had occurred in AE6002. Data are presented that allow the unambiguous identification of a second Fat gene (fatB) in C. crescentus. The map position of another mutation in membrane lipid biogenesis, the glycerol-3-PO4 auxotroph gpsA505, was also determined. During this study the flaZ gene was fine-mapped and the positions of proC and rif changed from the previously reported location.
GENETIC ANALYSIS OF NATURAL POPULATIONS OF DROSOPHILA MELANOGASTER IN JAPAN. IV. NATURAL SELECTION ON THE INDUCIBILITY, BUT NOT ON THE STRUCTURAL GENES, OF AMYLASE LOCI
Authors: Matsuo Yoshinori , Yamazaki Tsuneyuki
Published: January 2021

To test the validity of previous results the inducibility of amylase as well as other biochemical parameters was measured using 45 homozygous strains of Drosophila melanogaster from Akayu, Japan. Only the inducibility (but not protein contents or specific activity of the enzyme) was highly correlated with productivity measured using a starch food regime (rp = 0.41, P < 0.005, rg = 0.73 ± 0.21). Inducibility was also negatively correlated with developmental time using starch food; namely, the one with high inducibility developed the fastest. Population cage experiments using 1600 genomes from the same natural population showed that the inducibility responded positively to natural selection (1.6-fold increase in inducibility in cages using starch food relative to those using normal food), but little frequency change of allozymes was observed. All of these results were consistent and indicated that polymorphisms of inducing factors or regulatory genes were major determinants of fitness differences in a particular environment and may be the genetic materials responsible for the adaptive evolution of organisms, at least in amylase loci.
REARRANGEMENT OF THE GENETIC MAP OF CHROMOSOME VII OF SACCHAROMYCES CEREVISIAE
Authors: Celenza John L , Carlson Marian
Published: January 2021

The genetic map of the right arm of chromosome VII of Saccharomyces cerevisiae includes markers on a distal segment for which meiotic linkage to the centromere-proximal marker cly8 has not previously been demonstrated. According to the currently accepted map, SUF4 is the most distal marker on the right arm. We have shown by tetrad analysis that SUF4 is linked to cly8 and ade6. The genetic distance between SUF4 and cly8 is 29 cM. These data indicate that the genetic map of the right arm of chromosome VII should be revised by inverting the orientation of the distal segment so that SUF4 is located near cly8, and SUC1 and MAL1 are the most distal markers. With this revision, all of the polymeric fermentation markers that have been mapped are located at the ends of chromosomes.
INTERACTING GENES CONTROL GLYCEROL-3-PHOSPHATE DEHYDROGENASE EXPRESSION IN DEVELOPING CEREBELLUM OF THE MOUSE
Authors: Kozak Leslie P
Published: January 2021

The cerebellum of BALB/cJ mice has approximately 2.5 times as much glycerol-3-phosphate dehydrogenase (GPDH) as that of C57BL/6J mice. This difference in enzyme levels, which positively correlates with similar differences in the levels of hybridizable GPDH mRNA, is controlled by at least two unlinked regulatory loci and the structural gene, Gdc-1, located on chromosome 15. These regulatory loci, which act predominantly during the second and third weeks of postnatal cerebellar development and differentiation, have been separated from each other in the CXB recombinant inbred strains of mice. One regulatory locus, Gdcr-1, although unlinked to the structural gene, has an allele in BALB/c mice that preferentially enhances expression of the BALB/c structural allele at Gdc-1. The other locus, Gdcr-2, which may or may not be single, enhances GPDH expression at Gdc-1 irrespective of the allele present, as is commonly observed for loci acting from a distance. Measurements of GPDH mRNA in the recombinant inbred mice suggest that these regulatory genes act by modulating mRNA levels. Accordingly, the regulation of GPDH expression in the cerebellum of mice depends on a complex interaction of unlinked regulatory elements with regulatory elements near the structural gene. Furthermore, since the Gdc-1 locus is expressed in virtually every tissue of the mouse except blood and since the observed genetic variation is restricted to the cerebellum, it is likely that other tissues will have their own distinctive genetic mechanisms for modulating Gdc-1 expression.
BACTERIOPHAGE T4 GENE 32 PARTICIPATES IN EXCISION REPAIR AS WELL AS RECOMBINATIONAL REPAIR OF UV DAMAGES
Authors: Mosig Gisela
Published: January 2021

Gene 32 of phage T4 has been shown previously to be involved in recombinational repair of UV damages but, based on a mutant study, was thought not to be required for excision repair. However, a comparison of UV-inactivation curves of several gene 32 mutants grown under conditions permissive for progeny production in wild-type or polA  - hosts demonstrates that gene 32 participates in both kinds of repair. Different gene 32 mutations differentially inactivate these repair functions. Under conditions permissive for DNA replication and progeny production, all gene 32 mutants investigated here are partially defective in recombinational repair, whereas only two of them, P7 and P401, are also defective in excision repair. P401 is the only mutant whose final slope of the inactivation curve is significantly steeper than that of wildtype T4. These results are discussed in terms of interactions of gp32, a single-stranded DNA-binding protein, with DNA and with other proteins.
RESOLUTION OF DICENTRIC CHROMOSOMES BY TY-MEDIATED RECOMBINATION IN YEAST
Authors: Surosky Richard T , Tye Bik-Kwoon
Published: January 2021

We have integrated a plasmid containing a yeast centromere, CEN5, into the HIS4 region of chromosome III by transformation. Of the three transformant colonies examined, none contained a dicentric chromosome, but all contained a rearranged chromosome III. In one transformant, rearrangement occurred by homologous recombination between two Ty elements; one on the left arm and the other on the right arm of chromosome III. This event produced a ring chromosome (ring chromosome III) of about 60 kb consisting of CEN3 and all other sequences between the two Ty elements. In addition, a linear chromosome (chromosome IIIA) consisting of sequences distal to the two Ty elements including CEN5, but lacking 60 kb of sequences from the centromeric region, was produced. Two other transformants also contain a similarly altered linear chromosome III as well as an apparently normal copy of chromosome III. These results suggest that dicentric chromosomes cannot be maintained in yeast and that dicentric structures must be resolved for the cell to survive.—The meiotic segregation properties of ring chromosome III and linear chromosome IIIA were examined in diploid cells which also contained a normal chromosome III. Chromosome IIIA and normal chromosome III disjoined normally, indicating that homology or parallel location of the centromeric regions of these chromosomes are not essential for proper meiotic segregation. In contrast, the 60-kb ring chromosome III, which is homologous to the centromeric region of the normal chromosome III, did not appear to pair with fidelity with chromosome III.
A MODEL OF DUPLICATIVE TRANSPOSITION AND GENE CONVERSION FOR REPETITIVE DNA FAMILIES
Authors: Ohta Tomoko
Published: January 2021

A model of duplicative transposition and gene conversion for the evolution of repetitive DNA families was studied. In this model, transposition and conversion (both unbiased) are assumed to occur both within and between the genomes in a diploid cell, and any degree of linkage intensity is incorporated. The transition equations for allelic and nonallelic identity coefficients have been formulated by using the previous results. The results are widely applicable to many repetitive sequences, from dispersed families like transposons to tightly linked multigene families. It has been shown through extensive numerical studies on equilibrium properties that duplicative transposition and gene conversion have very similar effects on nonallelic identity coefficients, but that allelism and allelic identity are greatly influenced by the relative rates of occurrence of the two processes.
MEIOTIC GENE CONVERSION MUTANTS IN SACCHAROMYCES CEREVISIAE. I. ISOLATION AND CHARACTERIZATION OF pms1-1 AND pms1-2
Authors: Williamson Marsha S , Game John C , Fogel Seymour
Published: January 2021

The pms1 mutants, isolated on the basis of sharply elevated meiotic prototroph frequencies for two closely linked his4 alleles, display pleiotropic phenotypes in meiotic and mitotic cells. Two isolates carrying recessive mutations in PMS1 were characterized. They identify a function required to maintain low postmeiotic segregation (PMS) frequencies at many heterozygous sites. In addition, they are mitotic mutators. In mutant diploids, spore viability is reduced, and among survivors, gene conversion and postmeiotic segregation frequencies are increased, but reciprocal exchange frequencies are not affected. The conversion event pattern is also dramatically changed in multiply marked regions in pms1 homozygotes. The PMS1 locus maps near MET4 on chromosome XIV. The PMS1 gene may identify an excision-resynthesis long patch mismatch correction function or a function that facilitates correction tract elongation. The PMS1 gene product may also play an important role in spontaneous mitotic mutation avoidance and correction of mismatches in heteroduplex DNA formed during spontaneous and UV-induced mitotic recombination. Based on meiotic recombination models emphasizing mismatch correction in heteroduplex DNA intermediates, this interpretation is favored, but alternative interpretations involving longer recombination intermediates in the mutants are also considered.
RAD52-INDEPENDENT MITOTIC GENE CONVERSION IN SACCHAROMYCES CEREVISIAE FREQUENTLY RESULTS IN CHROMOSOMAL LOSS
Authors: Haber James E , Hearn Mark
Published: January 2021

We have examined spontaneous, interchromosomal mitotic recombination events between his4 alleles in both Rad+ and rad52 strains of Saccharomyces cerevisiae. In Rad+ strains, 74% of the His+ prototrophs resulted from gene conversion events without exchange of flanking markers. In diploids homozygous for the rad52-1 mutation, the frequency of His+ prototroph formation was less than 5% of the wild-type value, and more than 80% of the gene conversion events were accompanied by an exchange of flanking markers. Most of the rad52 intragenic recombination events arose by gene conversion accompanied by an exchange of flanking markers and not by a simple reciprocal exchange between the his4A and his4C alleles. There were also profound effects on the kinds of recombinant products that were recovered. The most striking effect was that RAD52-independent mitotic recombination frequently results in the loss of one of the two chromosomes participating in the gene conversion event.
ESCHERICHIA COLI RHO FACTOR IS INVOLVED IN LYSIS OF BACTERIOPHAGE T4-INFECTED CELLS
Authors: Linder Claës H , Carlson Karin
Published: January 2021

A Rid (Rho interaction deficient) phenotype of bacteriophage T4 mutants was defined by cold-sensitive restriction (lack of plaque formation) on rho  + hosts carrying additional polar mutations in unrelated genes, coupled to suppression (plaque formation) in otherwise isogenic strains carrying either a polarity-suppressing rho or a multicopy plasmid expressing the rho  + allele. This suggests that the restriction may be due to lower levels of Rho than what is available to T4 in the suppressing strains.—Rid394×4 was isolated upon hydroxylamine mutagenesis and mapped in the t gene; other t mutants (and mot, as well as dda dexA double mutants) also showed a Rid phenotype. In liquid culture in strains that restricted plaque formation Rid394×4 showed strong lysis inhibition (a known t  - phenotype) but no prolonged phage production (another well-known t  - phenotype). This implies that when Rho is limiting the t mutant shuts off phage production at the normal time. Lysis inhibition was partially relieved, and phage production prolonged to varying extents depending on growth conditions in strains that allowed plaque formation. No significant effects on early gene expression were found. Apparently, both mutant (polarity-suppressing) and wild-type Rho can function in prolonging phage production and partially relieving lysis inhibition of Rid394×4 when present at a sufficiently high level, and Rho may play other role(s) in T4 development than in early gene regulation.
NOVEL NEMATODE AMBER SUPPRESSORS
Authors: Hodgkin Jonathan
Published: January 2021

Nine amber suppressor mutations were isolated in the nematode Caenorhabditis elegans by reverting amber alleles of a sex-determining gene, tra-3. One suppressor maps to a known locus, sup-5 III, but the other eight map to three new loci, sup-21 X (five alleles), sup-22 IV (two alleles) and sup-23 IV (one allele). Amber alleles of tra-3 and of a dumpy gene, dpy-20, were used to measure the efficiency of suppression; the sup-21 and the sup-22 alleles were both shown to be heterogeneous and generally weaker suppressors than sup-5 alleles, which are homogeneous. The spectrum of mutations suppressed by a strong sup-21 allele, e1957, was investigated and compared to the spectra for the amber suppressors sup-5 III and sup-7 X, using amber alleles in 13 assorted genes. Some of the differences between these spectra may be due to limited tissue specificity in sup-21 expression.—Suppression of dpy-20 was used to show that the sex-linked suppressors sup-7 and sup-21 are not dosage compensated in male (XO) relative to hermaphrodite (XX).—Several uses of amber suppressors are critically discussed: for identifying null mutations, for varying levels of gene activity and for detecting maternal mRNA.
ELEVATED LEVELS OF PETITE FORMATION IN STRAINS OF SACCHAROMYCES CEREVISIAE RESTORED TO RESPIRATORY COMPETENCE. I. ASSOCIATION OF BOTH HIGH AND MODERATE FREQUENCIES OF PETITE MUTANT FORMATION WITH THE PRESENCE OF ABERRANT MITOCHONDRIAL DNA
Authors: Evans R J , Oakley K M , Clark-Walker G D
Published: January 2021

When recently arisen spontaneous petite mutants of Saccharomyces cerevisiae are crossed, respiratory competent diploids can be recovered. Such restored strains can be divided into two groups having sectored or unsectored colony morphology, the former being due to an elevated level of spontaneous petite mutation. On the basis of petite frequency, the sectored strains can be subdivided into those with a moderate frequency (5-16%) and those with a high frequency (>60%) of petite formation. Each of the three categories of restored strains can be found on crossing two petites, suggesting either that the parental mutants contain a heterogeneous population of deleted mtDNAs at the time of mating or that different interactions can occur between the defective molecules. Restriction endonuclease analysis of mtDNA from restored strains that have a wild-type petite frequency showed that they had recovered a wild-type mtDNA fragmentation pattern. Conversely, all examined cultures from both categories of sectored strains contained aberrant mitochondrial genomes that were perpetuated without change over at least 200 generations. In addition, sectored colony siblings can have different aberrant mtDNAs. The finding that two sectored, restored strains from different crosses have identical but aberrant mtDNAs provides evidence for preferred deletion sites from the mitochondrial genome. Although it appears that mtDNAs from sectored strains invariably contain duplications, there is no apparent correlation between the size of the duplication and spontaneous petite frequency.
ELEVATED LEVELS OF PETITE FORMATION IN STRAINS OF SACCHAROMYCES CEREVISIAE RESTORED TO RESPIRATORY COMPETENCE. II. ORGANIZATION OF MITOCHONDRIAL GENOMES IN STRAINS HAVING HIGH AND MODERATE FREQUENCIES OF PETITE MUTANT FORMATION
Authors: Evans R J , Clark-Walker G D
Published: January 2021

Restriction enzyme analysis of aberrant mtDNA molecules in restored strains of Saccharomyces cerevisiae that display an elevated level of petite formation has shown the occurrence of novel junction fragments and nonstoichiometric amounts for some unaltered bands. Five aberrant mitochondrial genomes from high-frequency petite-forming (hfp) strains (>60% petites per generation) contain like-oriented duplications and single copy regions. High-frequency petite formation is postulated to arise from increased intramolecular recombination between duplicated segments. Mitochondrial DNA structures in two other hfp strains cannot be easily interpreted and might arise from intramolecular recombination.—Mitochondria DNA from moderate-frequency petite-forming (mfp) strains (5-16% petites per generation) contains inverted duplications in two cases. The elevated petite formation is postulated to arise from homologous recombination between directly repeated sequences. In mtDNA from one mfp strain, deletion end-points have been shown to overlap. Such deletion endpoint overlap is postulated to be required for the maintenance of the tandem duplication in hfp strains. Two regions of the wild-type mtDNA (between cyb and oli2 and between SrRNA and oxi2) appear to be dispensable for mitochondrial function.
THE MOLECULAR THROUGH ECOLOGICAL GENETICS OF ABNORMAL ABDOMEN IN DROSOPHILA MERCATORUM. I. BASIC GENETICS
Authors: Templeton Alan R , Crease Teresa J , Shah Faith
Published: January 2021

The abnormal abdomen syndrome (aa) in Drosophila mercatorum is characterized by the persistence of juvenilized cuticle on the adult abdomen. The aa phenotype is shown to depend on at least two X-linked genetic elements that are about one map unit apart near the centromeric end of the X chromosome. These two genetic elements are necessary for aa expression; one behaves as a dominant element and the other as a recessive. Overlaying these genetic studies upon molecular work reported elsewhere, it is argued that the dominant element is the presence of a 5 kb insertion in a majority of the X-linked repeats coding for the 28S ribosomal RNA. The recessive element appears to be a locus controlling differential replication of noninserted over inserted 28S genes during polytenization. The aa syndrome requires both the presence of the inserted repeats and the failure to preferentially amplify noninserted repeats. Given the necessary X-linked elements for aa, a variety of modifiers are revealed. First, aa expression in males is Y-linked, apparently corresponding to a deletion of the 18S/28S rDNA gene cluster normally found on the Y. Moreover, all major autosomes can modify the penetrance of aa.
SHORT GENE CONVERSIONS IN THE HUMAN FETAL GLOBIN GENE REGION: A BY-PRODUCT OF CHROMOSOME PAIRING DURING MEIOSIS?
Authors: Powers Patricia A , Smithies Oliver
Published: January 2021

DNA sequence comparisons of a 1200-base pair (bp) region in 14 human fetal globin genes in seven linked pairs reveal 31 nucleotide substitutions at positions where the fetal globin genes, G  y and A  y, usually differ. In each case, the newly substituted nucleotide is identical to the one found at the same position in the linked nonallelic gene. Most of these nucleotide substitutions are clearly the result of gene conversions, but 11 could be the result of either very short gene conversions or of point mutations. The unexpectedly frequent occurrence of these short gene conversions suggests that they may be the relics of some normal interaction between homologous but nonallelic DNA sequences, and we discuss the possibility that they result from interactions occurring between homologous sequences during the process of meiotic chromosome pairing.
MITOCHONDRIAL DNA SEQUENCE DIVERGENCE AMONG LYCOPERSICON AND RELATED SOLANUM SPECIES
Authors: McClean Phillip E , Hanson Maureen R
Published: January 2021

Sequence divergence among the mitochondrial (mt) DNA of nine Lycopersicon and two closely related Solanum species was estimated using the shared fragment method. A portion of each mt genome was highlighted by probing total DNA with a series of plasmid clones containing mt-specific DNA fragments from Lycopersicon pennellii. A total of 660 fragments were compared. As calculated by the shared fragment method, sequence divergence among the mtDNAs ranged from 0.4% for the L. esculentum-L. esculentum var. cerasiforme pair to 2.7% for the Solanum rickii-L. pimpinellifolium and L. cheesmanii-L. chilense pairs. The mtDNA divergence is higher than that reported for Lycopersicon chloroplast (cp) DNA, which indicates that the DNAs of the two plant organelles are evolving at different rates. The percentages of shared fragments were used to construct a phenogram that illustrates the present-day relationships of the mtDNAs. The mtDNA-derived phenogram places L. hirsutum closer to L. esculentum than taxonomic and cpDNA comparisons. Further, the recent assignment of L. pennellii to the genus Lycopersicon is supported by the mtDNA analysis.
FRAMESHIFT SUPPRESSION IN AMINOACYL-tRNA LIMITED CELLS
Authors: Weiss Robert B , Gallant Jonathan A
Published: January 2021

Under certain conditions aminoacyl-tRNA limitation can phenotypically suppress frameshift alleles. The observed suppression is due to an increase in abnormal translocation of ribosomes translating codons that have a short supply of aminoacyl-tRNA. The rIIB frameshift alleles of bacteriophage T4 are used here to pinpoint the sites of ribosome frameshifting caused by these hypothetical decoding errors. The data indicate that not all hungry codons are associated with abnormal translocation, only a relatively small subset. Analysis of the hungry codons which are associated with ribosome frameshifting points to the existence of severe context effects determining the shiftiness of these codons.