bluuebunny/crossref_metadata_2025 huggingface dataset:
Whole-Genome Scan in Thelytokous-Laying Workers of the Cape Honeybee (Apis mellifera capensis): Central Fusion, Reduced Recombination Rates and Centromere Mapping Using Half-Tetrad Analysis
Authors: Baudry Emmanuelle , Kryger Per , Allsopp Mike , Koeniger Nikolaus , Vautrin Dominique , Mougel Florence , Cornuet Jean-Marie , Solignac Michel
Published: August 2004

While workers of almost all subspecies of honeybee are able to lay only haploid male eggs, Apis mellifera capensis workers are able to produce diploid female eggs by thelytokous parthenogenesis. Cytological analyses have shown that during parthenogenesis, egg diploidy is restored by fusion of the two central meiotic products. This peculiarity of the Cape bee preserves two products of a single meiosis in the daughters and can be used to map centromere positions using half-tetrad analysis. In this study, we use the thelytokous progenies of A. m. capensis workers and a sample of individuals from a naturally occurring A. m. capensis thelytokous clone to map centromere position for most of the linkage groups of the honeybee. We also show that the recombination rate is reduced by >10-fold during the meiosis of A. m. capensis workers. This reduction is restricted to thelytokous parthenogenesis of capensis workers and is not observed in the meiosis of queen within the same subspecies or in arrhenotokous workers of another subspecies. The reduced rate of recombination seems to be associated with negative crossover interference. These results are discussed in relation to evolution of thelytokous parthenogenesis and maintenance of heterozygosity and female sex after thelytoky.
A Microsatellite-Based Linkage Map of the Honeybee, Apis mellifera L.
Authors: Solignac Michel , Vautrin Dominique , Baudry Emmanuelle , Mougel Florence , Loiseau Anne , Cornuet Jean-Marie
Published: August 2004

A linkage map for the honeybee (Apis mellifera) was constructed mainly from the progeny of two hybrid queens (A. m. ligustica × A. m. mellifera). A total of 541 loci were mapped; 474 were microsatellite loci; a few were additional bands produced during PCRs, one of the two rDNA loci (using ITS), the MDH locus, and three sex-linked markers (Q and FB loci and one RAPD band). Twenty-four linkage groups were estimated of which 5 were minute (between 7.1 and 22.8 cM) and 19 were major groups (>76.5 cM). The number of major linkage groups exceeded by three the number of chromosomes of the complement (n = 16). The sum of the lengths of all linkage groups amounts to 4061 cM to which must be added at least 320 cM to link groups in excess, making a total of at least 4381 cM. The length of the largest linkage group I was 630 cM. The average density of markers was 7.5 cM and the average resolution was about one marker every 300 kb. For most of the large groups, the centromeric region was determined genetically, as described in Baudry  et al. (2004, accompanying article in this issue), using half-tetrad analysis of thelytokous parthenogens in which diploid restoration occurs through central fusion. Several cases of segregation distortion that appreared to result from deleterious recessives were discovered. A low positive interference was also detected.
Mutational Analysis of the Drosophila DNA Repair and Recombination Gene mei-9
Authors: Yıldız Özlem , Kearney Hutton , Kramer Benjamin C , Sekelsky Jeff J
Published: August 2004

Drosophila mei-9 is essential for several DNA repair and recombination pathways, including nucleotide excision repair (NER), interstrand crosslink repair, and meiotic recombination. To better understand the role of MEI-9 in these processes, we characterized 10 unique mutant alleles of mei-9. These include a P-element insertion that disrupts repair functions but not the meiotic function; three nonsense mutations, one of which has nearly wild-type levels of protein; three missense mutations, one of which disrupts the meiotic function but not repair functions; two small in-frame deletions; and one frameshift.
Genetic Mapping of Sexual Isolation Between E and Z Pheromone Strains of the European Corn Borer (Ostrinia nubilalis)
Authors: Dopman Erik B , Bogdanowicz Steven M , Harrison Richard G
Published: August 2004

The E and Z pheromone strains of the European corn borer (ECB) provide an exceptional model system for examining the genetic basis of sexual isolation. Differences at two major genes account for variation in female pheromone production and male behavioral response, components of the pheromone communication system known to be important for mate recognition and mate choice. Strains of ECB are morphologically indistinguishable, and surveys of allozyme and DNA sequence variation have revealed significant allele frequency differences at only a single sex-linked locus, Tpi. Here we present a detailed genetic linkage map of ECB using AFLP and microsatellite markers and map the factors responsible for pheromone production (Pher) and male response (Resp). Our map covers 1697 cM and identifies all 31 linkage groups in ECB. Both Resp and Tpi map to the Z (sex) chromosome, but the distance between these markers (>20 cM) argues against the hypothesis that patterns of variation at Tpi are explained by tight linkage to this “speciation gene.” However, we show, through analysis of marker density, that Tpi is located in a region of low recombination and suggest that a second Z-linked reproductive barrier could be responsible for the origin and/or persistence of differentiation at Tpi.
An F1 Genetic Screen for Maternal-Effect Mutations Affecting Embryonic Pattern Formation in Drosophila melanogaster
Authors: Luschnig Stefan , Moussian Bernard , Krauss Jana , Desjeux Isabelle , Perkovic Josip , Nüsslein-Volhard Christiane
Published: August 2004

Large-scale screens for female-sterile mutations have revealed genes required maternally for establishment of the body axes in the Drosophila embryo. Although it is likely that the majority of components involved in axis formation have been identified by this approach, certain genes have escaped detection. This may be due to (1) incomplete saturation of the screens for female-sterile mutations and (2) genes with essential functions in zygotic development that mutate to lethality, precluding their identification as female-sterile mutations. To overcome these limitations, we performed a genetic mosaic screen aimed at identifying new maternal genes required for early embryonic patterning, including zygotically required ones. Using the Flp-FRT technique and a visible germline clone marker, we developed a system that allows efficient screening for maternal-effect phenotypes after only one generation of breeding, rather than after the three generations required for classic female-sterile screens. We identified 232 mutants showing various defects in embryonic pattern or morphogenesis. The mutants were ordered into 10 different phenotypic classes. A total of 174 mutants were assigned to 86 complementation groups with two alleles on average. Mutations in 45 complementation groups represent most previously known maternal genes, while 41 complementation groups represent new loci, including several involved in dorsoventral, anterior-posterior, and terminal patterning.
A Physically Anchored Genetic Map and Linkage to Avirulence Reveals Recombination Suppression Over the Proximal Region of Hessian Fly Chromosome A2
Authors: Behura Susanta K , Valicente Fernando H , Rider S Dean , Shun-Chen Ming , Jackson Scott , Stuart Jeffrey J
Published: August 2004

Resistance in wheat (Triticum aestivum) to the Hessian fly (Mayetiola destructor), a major insect pest of wheat, is based on a gene-for-gene interaction. Close linkage (3 ± 2 cM) was discovered between Hessian fly avirulence genes vH3 and vH5. Bulked segregant analysis revealed two DNA markers (28-178 and 23-201) within 10 cM of these loci and only 3 ± 2 cM apart. However, 28-178 was located in the middle of the short arm of Hessian fly chromosome A2 whereas 23-201 was located in the middle of the long arm of chromosome A2, suggesting the presence of severe recombination suppression over its proximal region. To further test that possibility, an AFLP-based genetic map of the Hessian fly genome was constructed. Fluorescence in situ hybridization of 20 markers on the genetic map to the polytene chromosomes of the Hessian fly indicated good correspondence between the linkage groups and the four Hessian fly chromosomes. The physically anchored genetic map is the first of any gall midge species. The proximal region of mitotic chromosome A2 makes up 30% of its length but corresponded to <3% of the chromosome A2 genetic map.
Reduced Variation on the Chicken Z Chromosome
Authors: Sundström Hannah , Webster Matthew T , Ellegren Hans
Published: August 2004

Understanding the population genetic factors that shape genome variability is pivotal to the design and interpretation of studies using large-scale polymorphism data. We analyzed patterns of polymorphism and divergence at Z-linked and autosomal loci in the domestic chicken (Gallus gallus) to study the influence of mutation, effective population size, selection, and demography on levels of genetic diversity. A total of 14 autosomal introns (8316 bp) and 13 Z-linked introns (6856 bp) were sequenced in 50 chicken chromosomes from 10 highly divergent breeds. Genetic variation was significantly lower at Z-linked than at autosomal loci, with one segregating site every 39 bp at autosomal loci (θW = 5.8 ± 0.8 × 10–3) and one every 156 bp on the Z chromosome (θW = 1.4 ± 0.4 × 10–3). This difference may in part be due to a low male effective population size arising from skewed reproductive success among males, evident both in the wild ancestor—the red jungle fowl—and in poultry breeding. However, this effect cannot entirely explain the observed three- to fourfold reduction in Z chromosome diversity. Selection, in particular selective sweeps, may therefore have had an impact on reducing variation on the Z chromosome, a hypothesis supported by the observation of heterogeneity in diversity levels among loci on the Z chromosome and the lower recombination rate on Z than on autosomes. Selection on sex-linked genes may be particularly important in organisms with female heterogamety since the heritability of sex-linked sexually antagonistic alleles advantageous to males is improved when fathers pass a Z chromosome to their sons.
Insights Into Recombination From Patterns of Linkage Disequilibrium in Humans
Authors: Ptak Susan E , Voelpel Kristian , Przeworski Molly
Published: August 2004

An ability to predict levels of linkage disequilibrium (LD) between linked markers would facilitate the design of association studies and help to distinguish between evolutionary models. Unfortunately, levels of LD depend crucially on the rate of recombination, a parameter that is difficult to measure. In humans, rates of genetic exchange between markers megabases apart can be estimated from a comparison of genetic and physical maps; these large-scale estimates can then be interpolated to predict LD at smaller (“local”) scales. However, if there is extensive small-scale heterogeneity, as has been recently proposed, local rates of recombination could differ substantially from those averaged over much larger distances. We test this hypothesis by estimating local recombination rates indirectly from patterns of LD in 84 genomic regions surveyed by the SeattleSNPs project in a sample of individuals of European descent and of African-Americans. We find that LD-based estimates are significantly positively correlated with map-based estimates. This implies that large-scale, average rates are informative about local rates of recombination. Conversely, although LD-based estimates are based on a number of simplifying assumptions, it appears that they capture considerable information about the underlying recombination rate or at least about the ordering of regions by recombination rate. Using LD-based estimators, we also find evidence for homologous gene conversion in patterns of polymorphism. However, as we demonstrate by simulation, inferences about gene conversion are unreliable, even with extensive data from homogeneous regions of the genome, and are confounded by genotyping error.
Characterization of Epistasis Influencing Complex Spontaneous Obesity in the BSB Model
Authors: Yi Nengjun , Diament Adam , Chiu Sally , Kim Kyoungmi , Allison David B , Fisler Janis S , Warden Craig H
Published: August 2004

There is growing awareness that complex interactions among multiple genes and environmental factors play an important role in controlling obesity traits. The BSB mouse, which is produced by the backcross of (lean C57BL/6J × lean Mus spretus) × C57BL/6J, provides an excellent model of epistatic obesity. To evaluate potential epistatic interactions among six chromosomal regions previously determined to influence obesity phenotypes, we performed novel Bayesian analyses on the basis of both epistatic and nonepistatic models for four obesity traits: percentage of body fat, adiposity index, total fat mass, and body weight, and also for plasma total cholesterol. The epistatic analysis detected at least one more QTL than the nonepistatic analysis did for all obesity traits. These obesity traits were variously influenced by QTL on chromosomes 2, 7, 12, 15, and 16. Interaction between genes on chromosomes 2 and 12 was present for all obesity traits, accounting for 3–4.8% of the phenotypic variation. Chromosome 12 was found to have weak main effects on all obesity traits. Several different epistatic interactions were also detected for percentage of body fat, adiposity index, and total fat mass. Chromosomes 6 and 12 have not only main effects but also strong epistatic effects on plasma total cholesterol. Our results emphasize the importance of modeling epistasis for discovery of obesity genes.
Nucleotide Variation at Msn and Alas2, Two Genes Flanking the Centromere of the X Chromosome in Humans
Authors: Nachman Michael W , D'Agostino Susan L , Tillquist Christopher R , Mobasher Zahra , Hammer Michael F
Published: August 2004

The centromeric region of the X chromosome in humans experiences low rates of recombination over a considerable physical distance. In such a region, the effects of selection may extend to linked sites that are far away. To investigate the effects of this recombinational environment on patterns of nucleotide variability, we sequenced 4581 bp at Msn and 4697 bp at Alas2, two genes situated on either side of the X chromosome centromere, in a worldwide sample of 41 men, as well as in one common chimpanzee and one orangutan. To investigate patterns of linkage disequilibrium (LD) across the centromere, we also genotyped several informative sites from each gene in 120 men from sub-Saharan Africa. By studying X-linked loci in males, we were able to recover haplotypes and study long-range patterns of LD directly. Overall patterns of variability were remarkably similar at these two loci. Both loci exhibited (i) very low levels of nucleotide diversity (among the lowest seen in the human genome); (ii) a strong skew in the distribution of allele frequencies, with an excess of both very-low and very-high-frequency derived alleles in non-African populations; (iii) much less variation in the non-African than in the African samples; (iv) very high levels of population differentiation; and (v) complete LD among all sites within loci. We also observed significant LD between Msn and Alas2 in Africa, despite the fact that they are separated by ∼10 Mb. These observations are difficult to reconcile with a simple demographic model but may be consistent with positive and/or purifying selection acting on loci within this large region of low recombination.
Genetics of Barley Hooded Suppression
Authors: Roig Cristina , Pozzi Carlo , Santi Luca , Müller Judith , Wang Yamei , Stile Maria Rosaria , Rossini Laura , Stanca Michele , Salamini Francesco
Published: August 2004

The molecular basis of the barley dominant Hooded (K) mutant is a duplication of 305 bp in intron IV of the homeobox gene Bkn3. A chemical mutagenesis screen was carried out to identify genetical factors that participate in Bkn3 intron-mediated gene regulation. Plants from recurrently mutagenized KK seeds were examined for the suppression of the hooded awn phenotype induced by the K allele and, in total, 41 suK (suppressor of K) recessive mutants were identified. Complementation tests established the existence of five suK loci, and alleles suKB-4, suKC-33, suKD-25, suKE-74, and suKF-76 were studied in detail. All K-suppressed mutants showed a short-awn phenotype. The suK loci have been mapped by bulked segregant analysis nested in a standard mapping procedure based on AFLP markers. K suppressor loci suKB, B, E, and F all map in a short interval of chromosome 7H, while the locus suKD is assigned to chromosome 5H. A complementation test between the four suK mutants mapping on chromosome 7H and the short-awn mutant lks2, located nearby, excluded the allelism between suK loci and lks2. The last experiment made clear that the short-awn phenotype of suK mutants is due to a specific dominant function of the K allele, a function that is independent from the control on hood formation. The suK loci are discussed as candidate participants in the regulation of Bkn3 expression.
Comparative Mapping and Rapid Karyotypic Evolution in the Genus Helianthus
Authors: Burke John M , Lai Zhao , Salmaso Marzia , Nakazato Takuya , Tang Shunxue , Heesacker Adam , Knapp Steven J , Rieseberg Loren H
Published: August 2004

Comparative genetic linkage maps provide a powerful tool for the study of karyotypic evolution. We constructed a joint SSR/RAPD genetic linkage map of the Helianthus petiolaris genome and used it, along with an integrated SSR genetic linkage map derived from four independent H. annuus mapping populations, to examine the evolution of genome structure between these two annual sunflower species. The results of this work indicate the presence of 27 colinear segments resulting from a minimum of eight translocations and three inversions. These 11 rearrangements are more than previously suspected on the basis of either cytological or genetic map-based analyses. Taken together, these rearrangements required a minimum of 20 chromosomal breakages/fusions. On the basis of estimates of the time since divergence of these two species (750,000–1,000,000 years), this translates into an estimated rate of 5.5–7.3 chromosomal rearrangements per million years of evolution, the highest rate reported for any taxonomic group to date.
Genetic Variation at the Tomato Cf-4/Cf-9 Locus Induced by EMS Mutagenesis and Intralocus Recombination
Authors: Wulff Brande B H , Thomas Colwyn M , Parniske Martin , Jones Jonathan D G
Published: August 2004

The interaction between tomato (Lycopersicon esculentum) and the leaf mold pathogen Cladosporium fulvum is an excellent model for investigating disease resistance gene evolution. The interaction is controlled in a gene-for-gene manner by Cf genes that encode type I transmembrane extracellular leucinerich repeat glycoproteins that recognize their cognate fungal avirulence (Avr) proteins. Cf-4 from L. hirsutum and Cf-9 from L. pimpinellifolium are located at the same locus on the short arm of tomato chromosome 1 in an array of five paralogs. Molecular analysis has shown that one mechanism for generating sequence variation in Cf genes is intragenic sequence exchange through unequal crossing over or gene conversion. To investigate this we used a facile genetic selection to identify novel haplotypes in the progeny of Cf-4/Cf-9 trans-heterozygotes that lacked Cf-4 and Cf-9. This selection is based on the ability of Avr4 and Avr9 to induce Cf-4- or Cf-9-dependent seedling death. The crossovers were localized to the same intergenic region defining a recombination hotspot in this cross. As part of a structure-function analysis of Cf-9 and Cf-4, nine EMS-induced mutant alleles have been characterized. Most mutations result in single-amino-acid substitutions in their C terminus at residues that are conserved in other Cf proteins.
Comparative Population Genetics of the Panicoid Grasses: Sequence Polymorphism, Linkage Disequilibrium and Selection in a Diverse Sample of Sorghum bicolor
Authors: Hamblin Martha T , Mitchell Sharon E , White Gemma M , Gallego Javier , Kukatla Rakesh , Wing Rod A , Paterson Andrew H , Kresovich Stephen
Published: August 2004

Levels of genetic variation and linkage disequilibrium (LD) are critical factors in association mapping methods as well as in identification of loci that have been targets of selection. Maize, an outcrosser, has a high level of sequence variation and a limited extent of LD. Sorghum, a closely related but largely self-pollinating panicoid grass, is expected to have higher levels of LD. As a first step in estimation of population genetic parameters in sorghum, we surveyed 27 diverse S. bicolor accessions for sequence variation at a total of 29,186 bp in 95 short regions derived from genetically mapped RFLPs located throughout the genome. Consistent with its higher level of inbreeding, the extent of LD is at least severalfold greater in sorghum than in maize. Total sequence variation in sorghum is about fourfold lower than that in maize, while synonymous variation is fivefold lower, suggesting a smaller effective population size in sorghum. Because we surveyed a species-wide sample, the mating system, which primarily affects population-level diversity, may not be primarily responsible for this difference. Comparisons of polymorphism and divergence suggest that both directional and diversifying selection have played important roles in shaping variation in the sorghum genome.
Frequency-Dependent Selection With Dominance: A Window Onto the Behavior of the Mean Fitness
Authors: Asmussen Marjorie A , Cartwright Reed A , Spencer Hamish G
Published: August 2004

Selection in which fitnesses vary with the changing genetic composition of the population may facilitate the maintenance of genetic diversity in a wide range of organisms. Here, a detailed theoretical investigation is made of a frequency-dependent selection model, in which fitnesses are based on pairwise interactions between the two phenotypes at a diploid, diallelic, autosomal locus with complete dominance. The allele frequency dynamics are fully delimited analytically, along with all possible shapes of the mean fitness function in terms of where it increases or decreases as a function of the current allele frequency in the population. These results in turn allow possibly the first complete characterization of the dynamical behavior by the mean fitness through time under frequency-dependent selection. Here the mean fitness (i) monotonically increases, (ii) monotonically decreases, (iii) initially increases and then decreases, or (iv) initially decreases and then increases as equilibrium is approached. We analytically derive the exact initial and fitness conditions that produce each dynamic and how often each arises. Computer simulations with random initial conditions and fitnesses reveal that the potential decline in mean fitness is not negligible; on average a net decrease occurs 20% of the time and reduces the mean fitness by >17%.
In Vivo Analysis of Synaptonemal Complex Formation During Yeast Meiosis
Authors: White Eric J , Cowan Carrie , Cande W Zacheus , Kaback David B
Published: August 2004

During meiotic prophase a synaptonemal complex (SC) forms between each pair of homologous chromosomes and is believed to be involved in regulating recombination. Studies on SCs usually destroy nuclear architecture, making it impossible to examine the relationship of these structures to the rest of the nucleus. In Saccharomyces cerevisiae the meiosis-specific Zip1 protein is found throughout the entire length of each SC. To analyze the formation and structure of SCs in living cells, a functional ZIP1::GFP fusion was constructed and introduced into yeast. The ZIP1::GFP fusion produced fluorescent SCs and rescued the spore lethality phenotype of zip1 mutants. Optical sectioning and fluorescence deconvolution light microscopy revealed that, at zygotene, SC assembly was initiated at foci that appeared uniformly distributed throughout the nuclear volume. At early pachytene, the full-length SCs were more likely to be localized to the nuclear periphery while at later stages the SCs appeared to redistribute throughout the nuclear volume. These results suggest that SCs undergo dramatic rearrangements during meiotic prophase and that pachytene can be divided into two morphologically distinct substages: pachytene A, when SCs are perinuclear, and pachytene B, when SCs are uniformly distributed throughout the nucleus. ZIP1::GFP also facilitated the enrichment of fluorescent SC and the identification of meiosis-specific proteins by MALDI-TOF mass spectroscopy.
Mutators in Space: The Dynamics of High-Mutability Clones in a Two-Patch Model
Authors: Travis E R , Travis J M J
Published: August 2004

Clones of bacteria possessing high-mutability rates (or mutators) are being observed in an increasing number of species. In a constant environment most mutations are deleterious, and hence the spontaneous mutation rate is generally low. However, mutators may play an important role in the adaptation of organisms to changing environments. To date, theoretical work has focused on temporal variability in the environment, implicitly assuming that environmental conditions are constant through space. Here, we develop a two-patch model to investigate how spatiotemporal environmental variability and dispersal might influence mutator dynamics. Environmental conditions in each patch fluctuate between two states; the rate of fluctuation varies in each patch at differing phase angles. We find that at low and intermediate rates of fluctuation, an increase in dispersal results in a decrease in the density of mutators. However, at high rates of environmental change, dispersal causes an increase in mutator density. For all frequencies of environmental fluctuation these trends are enhanced as the phase angle approaches 180°. We argue that future work, both empirical and theoretical, is needed to improve our understanding of how spatiotemporal variability impacts on mutator densities and dynamics.
Stochastic Gene Expression in Fluctuating Environments
Authors: Thattai Mukund , van Oudenaarden Alexander
Published: August 2004

Stochastic mechanisms can cause a group of isogenic bacteria, each subject to identical environmental conditions, to nevertheless exhibit diverse patterns of gene expression. The resulting phenotypic subpopulations will typically have distinct growth rates. This behavior has been observed in several contexts, including sugar metabolism and pili phase variation. Under fixed environmental conditions, the net growth rate of the population is maximized when all cells are of the fastest growing phenotype, so it is unclear what fitness advantage is conferred by population heterogeneity. However, unlike ideal laboratory conditions, natural environments tend to fluctuate, either periodically or randomly. Here we use a stochastic population model to show that, during growth in such fluctuating environments, a dynamically heterogenous bacterial population can sometimes achieve a higher net growth rate than a homogenous one. By using stochastic mechanisms to sample several distinct phenotypes, the bacteria are able to anticipate and take advantage of sudden changes in their environment. However, this heterogeneity is beneficial only if the bacterial response rate is sufficiently low. Our results could be useful in the design of artificial evolution experiments and in the optimization of fermentation processes.
Natural Selection Affects Frequencies of AG and GT Dinucleotides at the 5′ and 3′ Ends of Exons
Authors: Eskesen S T , Eskesen F N , Ruvinsky A
Published: August 2004

GT and AG, located at the 5′ and 3′ ends of introns, are important for correct splicing. It is anticipated that natural selection decreases frequency of AG and GT near the 5′ and 3′ ends of exons, preventing appearance of cryptic splicing sites. The data presented in this article support the expectation.
MrpL36p, a Highly Diverged L31 Ribosomal Protein Homolog With Additional Functional Domains in Saccharomyces cerevisiae Mitochondria
Authors: Williams Elizabeth H , Perez-Martinez Xochitl , Fox Thomas D
Published: August 2004

Translation in mitochondria utilizes a large complement of ribosomal proteins. Many mitochondrial ribosomal components are clearly homologous to eubacterial ribosomal proteins, but others appear unique to the mitochondrial system. A handful of mitochondrial ribosomal proteins appear to be eubacterial in origin but to have evolved additional functional domains. MrpL36p is an essential mitochondrial ribosomal large-subunit component in Saccharomyces cerevisiae. Increased dosage of MRPL36 also has been shown to suppress certain types of translation defects encoded within the mitochondrial COX2 mRNA. A central domain of MrpL36p that is similar to eubacterial ribosomal large-subunit protein L31 is sufficient for general mitochondrial translation but not suppression, and proteins bearing this domain sediment with the ribosomal large subunit in sucrose gradients. In contrast, proteins lacking the L31 domain, but retaining a novel N-terminal sequence and a C-terminal sequence with weak similarity to the Escherichia coli signal recognition particle component Ffh, are sufficient for dosage suppression and do not sediment with the large subunit of the ribosome. Interestingly, the activity of MrpL36p as a dosage suppressor exhibits gene and allele specificity. We propose that MrpL36p represents a highly diverged L31 homolog with derived domains functioning in mRNA selection in yeast mitochondria.
Phenotypic Plasticity in Bacterial Plasmids
Authors: Turner Paul E
Published: August 2004

Plasmid pB15 was previously shown to evolve increased horizontal (infectious) transfer at the expense of reduced vertical (intergenerational) transfer and vice versa, a key trade-off assumed in theories of parasite virulence. Whereas the models predict that susceptible host abundance should determine which mode of transfer is selectively favored, host density failed to mediate the trade-off in pB15. One possibility is that the plasmid's transfer deviates from the assumption that horizontal spread (conjugation) occurs in direct proportion to cell density. I tested this hypothesis using Escherichia coli/pB15 associations in laboratory serial culture. Contrary to most models of plasmid transfer kinetics, my data show that pB15 invades static (nonshaking) bacterial cultures only at intermediate densities. The results can be explained by phenotypic plasticity in traits governing plasmid transfer. As cells become more numerous, the plasmid's conjugative transfer unexpectedly declines, while the trade-off between transmission routes causes vertical transfer to increase. Thus, at intermediate densities the plasmid's horizontal transfer can offset selection against plasmid-bearing cells, but at high densities pB15 conjugates so poorly that it cannot invade. I discuss adaptive vs. nonadaptive causes for the phenotypic plasticity, as well as potential mechanisms that may lead to complex transfer dynamics of plasmids in liquid environments.
Genetic Interactions With C-Terminal Domain (CTD) Kinases and the CTD of RNA Pol II Suggest a Role for ESS1 in Transcription Initiation and Elongation in Saccharomyces cerevisiae
Authors: Wilcox Cathy B , Rossettini Anne , Hanes Steven D
Published: August 2004

Ess1 is an essential prolyl isomerase that binds the C-terminal domain (CTD) of Rpb1, the large subunit of RNA polymerase II. Ess1 is proposed to control transcription by isomerizing phospho-Ser-Pro peptide bonds within the CTD repeat. To determine which step(s) in the transcription cycle might require Ess1, we examined genetic interactions between ESS1 and genes encoding the known CTD kinases (KIN28, CTK1, BUR1, and SRB10). Although genetic interactions were identified between ESS1 and all four kinases, the clearest interactions were with CTK1 and SRB10. Reduced dosage of CTK1 rescued the growth defect of ess1ts mutants, while overexpression of CTK1 enhanced the growth defects of ess1ts mutants. Deletion of SRB10 suppressed ess1ts and ess1Δ mutants. The interactions suggest that Ess1 opposes the functions of these kinases, which are thought to function in preinitiation and elongation. Using a series of CTD substitution alleles, we also identified Ser5-Pro6 as a potential target for Ess1 isomerization within the first “half” of the CTD repeats. On the basis of the results, we suggest a model in which Ess1-directed conformational changes promote dephosphorylation of Ser5 to stimulate preinitiation complex formation and, later, to inhibit elongation.
Short Fiber Reinforced Hydroxyapatite‐based Bioceramics
Authors: Dorner‐Reisel A. , Müller E. , Tomandl G.
Published: August 2004

If hydroxyapatite‐based bioceramics should be exploited under load bearing conditions, mechanical properties, for instance fracture toughness and reliability, need to be improved. The following contribution relates own research results about short fiber reinforced hydroxyapatite for hard tissue engineering to actual developments in this field. In addition to mechanical properties, attention is given to methods of tailoring the fiber‐matrix interface, promoted decomposition of hydroxyapatite due to the fiber reinforcement, the presence of amorphous calcium phosphate and the biological behaviour.
Functional Cubic Thin Films — A Structure View
Authors: Rafaja D.
Published: August 2004

Real structure of materials influences their physical properties. Thus, the understanding of the relationship between the structure parameters and the materials properties is a necessary basis for materials design. X‐ray diffraction is a powerful experimental technique, which yields the required information about the microscopic and mesoscopic structure expressed in terms of lattice parameters, residual stress, microstrain, crystallite size, texture and crystal anisotropy. Application of advanced X‐ray methods and related computational procedures is illustrated on a detailed structure study of cubic uranium nitride thin films that shows the connection between the microscopic and the mesoscopic structure parameters.
Novel Dispersion Strengthened Metals by Mechanical Alloying
Authors: Martin U. , Heilmaier M.
Published: August 2004

Novel oxide dispersion strengthened (ODS) metals were synthesised by mechanical alloying (MA) and subsequent consolidation via hot pressing in protective argon atmosphere. The effect of dispersoid size and volume fraction on the electrical and mechanical properties is exemplified with Cr2O3, CaO and Y2O3 as model candidates for systematically studying the principles of particle selection by Groza and Gibeling. The results for the development of the microstructure under different processing conditions show that control of the impurity level is of primary importance for achieving high‐quality, fully dense material. Hence, a modified cryo‐milling technique at liquid N temperature was applied. The microstructure of such ultrafine‐grained (UFG) oxide dispersion strengthened silver and copper alloys was examined by means of TEM and high‐resolution scanning electron microscopy (HRSEM). Data at ambient temperature are presented, revealing that the mechanical and electrical properties can be tailored within a wide range as a function of the microstructure. These results are explained by microstructural concepts for room temperature yielding and electrical conductivity.
Influence of Vibration During Solidification of Molten Metals on Structure and Casting Properties
Authors: Bast J. , Hübler J. , Dommaschk C.
Published: August 2004

By a vibration treatment during the solidification process it is possible to change the structure. Model tests were accomplished in order to understand the procedures as deep as possible. On cylindrical samples the influence of a vibration treatment for the process of the solidification was examined. Pure aluminium and the eutectic alloy AlSi12 showed clear differences in the solidification course and in the casting structure.
Fatigue Strength of Heat‐treatable Steel Under Static Multiaxial Compression Stresses
Authors: Lüpfert H.‐P. , Spies H.‐J.
Published: August 2004

Known conceptions of calculation for consideration of the influence of mean stresses on the fatigue strength are discussed. While previously known models do not consider the changed fracture behaviour due to acting compressive mean stresses or otherwise accept compressive mean stresses only for the same direction of action with the cyclic load, the presented new conception allows the strength assessment of arbitrary multiaxial loads.
Structure and Properties as a Result of Electron Beam Surface Treatment
Authors: Zenker R.
Published: August 2004

A new generation of high frequency 3D deflection technique opens up manifold possibilities for a wider application of electron beam (EB) technologies for surface treatment. A high flexibility of process parameters connected with high productivity is obtained from the simultaneous interaction of the EB in several processing areas or by carrying out several processes simultaneously. The change of material and component‐specific surface properties can be adapted as required. An outstanding improvement of properties can be reached. Typical technological characteristics are explained and the influence of EB parameters on microstructure and properties is discussed. It has been shown that the EB is becoming more and more attractive and important for industrial applications of thermal surface technologies such as hardening, combined thermochemical treatment/hardening, remelting, surface alloying and dispersing
Materials and Process Development of Advanced Refractories for Innovative Metal Processing
Authors: Aneziris C.G. , Homola F. , Borzov D.
Published: August 2004

Improved structures of MgO carbon bonded materials due to new binder systems and due to the application of electrical currents during operation have been achieved for advanced applications in the secondary metallurgy and during near net shape metal casting.
Deformation Behaviour and Microstructure Development of Magnesium AZ 31 Alloy During Hot and Semi‐hot Deformation
Authors: Kawalla R. , Stolnikov A.
Published: August 2004

Deformation properties and microstructure development between 20 and 450 °C were investigated for Magnesium AZ31 alloy. It was found that this alloy softens preferably by dynamic recrystallisation. This process starts at suitable deformation conditions above 150 °C. However, the temperature region above 250 °C is more interesting for the production process the semi‐finished products. The recrystallised grain size depends heavily on the deformation temperature. A grain size with a mean diameter smaller than 10 μm can be created below 300 °C. For further processing of Magnesium sheets, temperatures above 100 °C are suitable, but temperatures above 300 °C are responsible for superplasticity.
Ceramic Membranes for Filtration Applications — Preparation and Characterization
Authors: Benfer S. , Árki P. , Tomandl G.
Published: August 2004

This article gives an overview about the preparation and characterization of asymmetric ceramic membranes that have been developed at our institute within the last years. Depending on the required pore size of the filter active layer for filtration applications ranging from microfiltration (MF) up to nanofiltration (NF) different preparation routes have to be applied.
Basic Mechanisms and Models of Multi‐Wire Sawing
Authors: Möller H.J.
Published: August 2004

More than 80 % of the current solar cell production requires the cutting of large silicon crystals. While in the last years the cost of solar cell processing and module fabrication could be reduced considerably, the sawing costs remain high, about 30 % of the wafer production. At present the large crystals are cut using the multi‐wire slicing technology[2]which has the advantage of a high throughput (several hundred wafers per day and machine), a small kerf loss of about 200 μm and almost no restrictions on the size of the ingots. Basic knowledge about the microscopic details of the sawing process is required in order to slice crystals in a controlled way. In the following the principles of the sawing process will be described in this review article as far as they are understood today.
Empirical and Data Based Modelling of Steel Technology Processes for Industrial Application
Authors: Scheller P.R. , Peisker D.
Published: August 2004

Process models and modelling of the fundamental relationships between the process parameters and the material properties are significant for process automation. Examples taken from the liquid steel treatment, the casting and solidification process and also from the microstructure formation and thermal influence of its properties show the practice oriented modelling of individual processing steps in the manufacturing of steel. Modelling is based both on physical and chemical fundamental principles and on data‐based methods. The used data are based on own empirical investigations as well as on selected published data which are collected in the own data base.
Fatigue Behaviour of Al‐Matrix Composites
Authors: Hartmann O. , Herrmann K. , Biermann H.
Published: August 2004

The cyclic deformation behaviour and fatigue lives of different Al‐matrix composites reinforced by alumina reinforcements were investigated under total strain control mode at room temperature. The composites differ in either matrix strength (peak aged vs. overaged AA6061 alloy and soft Al99.85, respectively) and/or type of reinforcement (particles, Saffil short fibres and Almax continuous fibres). The damage evolution was characterized by compliance experiments within individual stress‐strain hysteresis loops. The differences of the material behaviour are discussed with respect to matrix strength and reinforcement geometry.
Brachydactyly and short stature in a kindred with early‐onset parkinsonism
Authors: Dekker Marieke C.J. , Galjaard R.J.H. , Snijders P.J.L.M. , Heutink P. , Oostra B.A. , van Duijn C.M.
Published: August 2004

In a Dutch kindred we have identified a deletion of the DJ‐1 gene, leading to autosomal‐recessive parkinsonism. The parkinsonism patients also had short stature and brachydactyly. In the family and a control group from the same community, we used the DJ‐1 deletion as a marker for the originally linked PARK7 region and found a significant association with body height (P = 0.005), which suggests a gene in linkage disequilibrium with DJ‐1 to be implicated in short stature. Analysis of hand‐bone length showed incomplete segregation of the PARK7 region with brachydactyly, such that a gene in PARK7 is unlikely to fully explain the brachydactyly. Since the bone length reduction was more pronounced in the homozygous parkinsonism patients than in their heterozygous relatives, however, the PARK7 region may contain a modifier gene for growth. © 2004 Wiley‐Liss, Inc.
Activation of 5‐HT1B/1D receptor in the periaqueductal gray inhibits nociception
Authors: Bartsch T. , Knight Y. E. , Goadsby P. J.
Published: August 2004

It is considered that the site of action of the abortive antimigraine compounds acting at serotonin, 5‐HT1B/1D, receptors (triptans) is the trigeminovascular system. We tested whether there is a non‐trigeminal site of action. The 5‐HT1B/1D agonist, naratriptan, was microinjected into the ventrolateral periaqueductal gray (vlPAG), and activity in the trigeminal nucleus caudalis (TNC) was monitored. Recordings were made from 20 nociceptive neurons in the dorsal horn of the TNC that received convergent input from the dura mater and face. Responses of neurons to dural, facial cutaneous and corneal stimulation were studied before and after injection of naratriptan. Naratriptan decreased the excitability to electrical stimulation of the dura mater as the A‐fiber response decreased by 24 ± 4.1% (p < 0.001) and the C‐fiber response decreased by 42 ± 8.2% (p < 0.001). Spontaneous activity was decreased by 38 ± 7.5% (p < 0.001). After injection, the mechanical thresholds of the dura mater increased from (n = 14, p < 0.01). Responses to stimulation of the face and cornea were not altered by injection of naratriptan. These results suggest that 5‐HT1B/1D receptor activation in the vlPAG activates descending pain‐modulating pathways that inhibit dural, but not facial and corneal nociceptive input. These findings have implications for the understanding of the action of triptans in migraine and cluster headache, suggesting that brain loci other than the trigeminal nucleus may play a role in the clinical action of triptans. Ann Neurol 2004
Dissolution of softwood kraft pulps by direct derivatization in lithium chloride/N,N‐dimethylacetamide
Authors: Berthold Fredrik , Gustafsson Kristina , Berggren Rickard , Sjöholm Elisabeth , Lindström Mikael
Published: August 2004

A method for the characterization of the molar mass distributions (MMDs) of softwood kraft pulps dissolved in 0.5% lithium chloride (LiCl)/N,N‐dimethylacetamide (DMAc) by size exclusion chromatography is presented. The method is based on derivatization with ethyl isocyanate and the dissolution of samples in 8% LiCl/DMAc. In this study, the derivatization of hardwood kraft pulps did not influence the MMD. In the case of softwood pulps, however, the derivatization decreased the proportion of the high‐molecular‐mass material and increased the proportion of the low‐molecular‐mass material, which resulted in a distribution similar to the MMD of a hardwood kraft pulp. The results suggest that associations between hemicellulose and cellulose in the softwood kraft pulp were ruptured during derivatization. This led to a more correct estimation of the MMD of derivatized softwood kraft pulps than obtained by the dissolution of nonderivatized samples. This new method offers several advantages over derivatization with phenyl isocyanate: a precipitation step is not necessary, it is possible to follow the lignin distribution in the samples, and the method allows very high levels of dissolution of softwood kraft pulps up to a κ number of around 50. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 424–431, 2004
Miscibility studies on poly(ethylene glycol)/dextran blends in aqueous solutions by dilute solution viscometry
Authors: Kavlak Serap , Can Hatice Kaplan , Güner Ali
Published: August 2004

Miscibility of poly(ethylene glycol) (PEG) with dextran (Dx) was investigated by dilute solution viscometry. Dilute solution viscosity measurements were made on ternary systems, polymer (1)/polymer (2)/solvent (H2O), for four different average molecular weights of PEG and Dx. The intrinsic viscosity and viscometric interaction parameters were experimentally measured for the binary (solvent/polymer) as well as for the ternary systems by classical Huggins equation. Degree of miscibility of these polymer systems was estimated on the basis of the four following criteria: (1) the sign of the ΔkAB, (2) the sign of α, (3) the sign of ΔB, and (4) the sign of the μ. Based on the sign convention involved in these criteria, immiscibility was observed in most systems. The miscibility of all these systems in accordance with the interactions between the unlike polymer chains rather the polymer–solvent interactions were investigated depending on molecular weight of polymer sample. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 453–460, 2004