Cloning, mapping, and expression of ial, a novel Drosophila member of the Ipl1/aurora mitotic control kinase family.

The members of the Ipl1-aurora like kinase (IARK) subfamily are conserved serine/threonine kinases that play a key role in the control of chromosome segregation, centrosome separation, and cytokinesis from yeast to mammals. We report on the isolation of a new Drosophila member of the family, designated Ipl1-aurora-like kinase (ial) Phylogenetic analysis of kinase domains established that ial is more divergent from known mammalian IARKs than is aurora. Mapping based on examination of chromosomal aberrations, together with mapping within contigs identified by the Drosophila Genome Project, placed the gene at 32B on the left arm of the second chromosome. Discrete single-gene mutations in this region, including all known relevant P-element disruptions, were examined and proven not to be mutations in ial. Characterization of spatial and temporal expression of ial and its gene product showed that it manifests itself in patterns which can be consistent with a role in cell cycle control.     

Solution scattering studies of dimeric and tetrameric spectrin

The structure of spectrin dimers and tetramers in solution has been examined by light, low-angle X-ray and neutron scattering. The results show a good correspondence between the solution dimensions of these molecules and their appearance in the electron microscope after shadowing. The scattering profiles are not compatible with an extended rod-like character, but reflect the presence of a considerable degree of bending. The radii of gyration of the dimer and tetramer were determined to be 170 and 375 Å and the cross-section radii of gyration 14 and 12.3 Å. respectively. Both are thus long. thin. rather bent molecules, and the tetramer is twice the length of the dimer.     

Instability of transposase activity: Evidence from bacteriophage Mu DNA replication

Transposition of genetic elements involves coupled replication and integration events catalyzed in part by a class of proteins called transposases. We have asked whether the transposase activity of bacteriophage Mu (the Mu A protein) is stable and capable of catalyzing multiple rounds of coupled replication/integration, or whether its continued synthesis is required to maintain Mu DNA replication. Inhibition of protein synthesis during the lytic cycle with chloramphenicol inhibited Mu DNA synthesis with a half-life of approximately 3 min, demonstrating a need for continued protein synthesis to maintain Mu DNA replication. Synthesis of specific Mu-encoded proteins was inhibited by infecting a host carrying a temperature-sensitive suppressor, at permissive temperature, with Mu amber phages, then shifting to nonpermissive temperature. When Aam phages were used, Mu DNA replication was inhibited with kinetics essentially identical to those with chloramphenicol addition; hence, it is likely that continued synthesis of the Mu A protein is required to maintain Mu DNA replication. The data suggest that the activity of the Mu A protein is unstable, and raise the possibility that the Mu A protein and other transposases may be used stoichiometrically rather than catalytically.     

Consistent physiological,ecological and evolutionary effects of fire regime on conservative leaf economics strategies in plant communities

The functional response of plant communities to disturbance is hypothesised to be controlled by changes in environmental conditions and evolutionary history of species within the community. However, separating these influences using direct manipulations of repeated disturbances within ecosystems is rare. We evaluated how 41 years of manipulated fire affected plant leaf economics by sampling 89 plant species across a savanna-forest ecotone. Greater fire frequencies created a high-light and low-nitrogen environment, with more diverse communities that contained denser leaves and lower foliar nitrogen content. Strong trait–fire coupling resulted from the combination of significant intraspecific trait–fire correlations being in the same direction as interspecific trait differences arising through the turnover in functional composition along the fire-frequency gradient. Turnover among specific clades helped explain trait–fire trends, but traits were relatively labile. Overall, repeated burning led to reinforcing selective pressures that produced diverse plant communities dominated by conservative resource-use strategies and slow soil nitrogen cycling.     

Assessing the performance of qpAdm: a statistical tool for studying population admixture

qpAdm is a statistical tool for studying the ancestry of populations with histories that involve admixture between two or more source populations. Using qpAdm, it is possible to identify plausible models of admixture that fit the population history of a group of interest and to calculate the relative proportion of ancestry that can be ascribed to each source population in the model. Although qpAdm is widely used in studies of population history of human (and nonhuman) groups, relatively little has been done to assess its performance. We performed a simulation study to assess the behavior of qpAdm under various scenarios in order to identify areas of potential weakness and establish recommended best practices for use. We find that qpAdm is a robust tool that yields accurate results in many cases, including when data coverage is low, there are high rates of missing data or ancient DNA damage, or when diploid calls cannot be made. However, we caution against co-analyzing ancient and present-day data, the inclusion of an extremely large number of reference populations in a single model, and analyzing population histories involving extended periods of gene flow. We provide a user guide suggesting best practices for the use of qpAdm.     

Noncrossing quantile regression curve estimation

Since quantile regression curves are estimated individually, the quantile curves can cross, leading to an invalid distribution for the response. A simple constrained version of quantile regression is proposed to avoid the crossing problem for both linear and nonparametric quantile curves. A simulation study and a reanalysis of tropical cyclone intensity data shows the usefulness of the procedure. Asymptotic properties of the estimator are equivalent to the typical approach under standard conditions, and the proposed estimator reduces to the classical one if there is no crossing. The performance of the constrained estimator has shown significant improvement by adding smoothing and stability across the quantile levels.