We report an assessment of the ability of the Locally-Adaptive Model of Archaeological Potential (LAMAP) to estimate archaeological potential in relation to hunter-gatherer sites. The sample comprised 182 known sites in the Tanana Valley, Alaska, which was occupied solely by hunter-gatherers for about 14,500 years. To estimate archaeological potential, we employed physiographic variables such as elevation and slope, rather than variables that are known to vary on short time scales, like vegetation cover.
View Article and Find Full Text PDFEnvironmentally transformative human use of land accelerated with the emergence of agriculture, but the extent, trajectory, and implications of these early changes are not well understood. An empirical global assessment of land use from 10,000 years before the present (yr B.P.
View Article and Find Full Text PDFDisassembling microtubules can generate movement independently of motor enzymes, especially at kinetochores where they drive chromosome motility. A popular explanation is the 'conformational wave' model, in which protofilaments pull on the kinetochore as they curl outward from a disassembling tip. But whether protofilaments can work efficiently via this spring-like mechanism has been unclear.
View Article and Find Full Text PDFThe Ice Free Corridor has been invoked as a route for Pleistocene human and animal dispersals between eastern Beringia and more southerly areas of North America. Despite the significance of the corridor, there are limited data for when and how this corridor was used. Hypothetical uses of the corridor include: the first expansion of humans from Beringia into the Americas, northward postglacial expansions of fluted point technologies into Beringia, and continued use of the corridor as a contact route between the north and south.
View Article and Find Full Text PDFFactors that influence the orientation of the mitotic spindle are important for the maintenance of stem cell populations and in cancer development. However, screening for these factors requires rapid quantification of alterations of the angle of the mitotic spindle in cultured cell lines. Here we describe a method to image mitotic cells and rapidly score the angle of the mitotic spindle using a simple MATLAB application to analyze a stack of Z-images.
View Article and Find Full Text PDFMany proteins and protein complexes perform sophisticated, regulated functions in vivo. Many of these functions can be recapitulated using in vitro reconstitution, which serves as a means to establish unambiguous cause-effect relationships, for example, between a protein and its phosphorylating kinase. Here, we describe a protocol to purify kinetochores, the protein complexes that attach chromosomes to microtubules during mitosis, and quantitatively assay their microtubule-binding characteristics.
View Article and Find Full Text PDFPrecision analyses of the collective motor behaviors have become important to dissecting mechanisms underlying the trafficking of subcellular commodities in eukaryotic cells. Here, we describe a synthetic approach to create structurally defined multiple protein complexes containing two elastically coupled motor molecules. Motors are connected using a simple DNA-scaffolding molecule and DNA-conjugated, artificial protein polymers that function as tunable elastic linkers.
View Article and Find Full Text PDFIntracellular transport is a fundamental biological process during which cellular materials are driven by enzymatic molecules called motor proteins. Recent optical trapping experiments and theoretical analysis have uncovered many features of cargo transport by multiple kinesin motor protein molecules under applied loads. These studies suggest that kinesins cooperate negatively under typical transport conditions, although some productive cooperation could be achieved under higher applied loads.
View Article and Find Full Text PDFIntracellular transport is supported by enzymes called motor proteins that are often coupled to the same cargo and function collectively. Recent experiments and theoretical advances have been able to explain certain behaviors of multiple motor systems by elucidating how unequal load sharing between coupled motors changes how they bind, step, and detach. However, nonmechanical interactions are typically overlooked despite several studies suggesting that microtubule-bound kinesins interact locally via short-range nonmechanical potentials.
View Article and Find Full Text PDFCharacterization of the collective behaviors of different classes of processive motor proteins has become increasingly important to understand various intracellular trafficking and transport processes. This work examines the dynamics of structurally-defined motor complexes containing two myosin Va (myoVa) motors that are linked together via a molecular scaffold formed from a single duplex of DNA. Dynamic changes in the filament-bound configuration of these complexes due to motor binding, stepping, and detachment were monitored by tracking the positions of different color quantum dots that report the position of one head of each myoVa motor on actin.
View Article and Find Full Text PDFMicrotubule-dependent transport is most often driven by collections of kinesins and dyneins that function in either a concerted fashion or antagonistically. Several lines of evidence suggest that cargo transport may not be influenced appreciably by the combined action of multiple kinesins. Yet, as in previous optical trapping experiments, the forces imposed on cargos will vary spatially and temporally in cells depending on a number of local environmental factors, and the influence of these conditions has been largely overlooked.
View Article and Find Full Text PDFSubcellular cargos are often transported by teams of processive molecular motors, which raises questions regarding the role of motor cooperation in intracellular transport. Although our ability to characterize the transport behaviors of multiple-motor systems has improved substantially, many aspects of multiple-motor dynamics are poorly understood. This work describes a transition rate model that predicts the load-dependent transport behaviors of multiple-motor complexes from detailed measurements of a single motor's elastic and mechanochemical properties.
View Article and Find Full Text PDFThe number of microtubule motors attached to vesicles, organelles, and other subcellular commodities is widely believed to influence their motile properties. There is also evidence that cells regulate intracellular transport by tuning the number and/or ratio of motor types on cargos. Yet, the number of motors responsible for cargo motion is not easily characterized, and the extent to which motor copy number affects intracellular transport remains controversial.
View Article and Find Full Text PDFTransport of intracellular cargos by multiple microtubule motor proteins is believed to be a common and significant phenomenon in vivo, yet signatures of the microscopic dynamics of multiple motor systems are only now beginning to be resolved. Understanding these mechanisms largely depends on determining how grouping motors affect their association with microtubules and stepping rates, and hence, cargo run lengths and velocities. We examined this problem using a discrete state transition rate model of collective transport.
View Article and Find Full Text PDFThe collective function of motor proteins is known to be important for the directed transport of many intracellular cargos. However, understanding how multiple motors function as a group remains challenging and requires new methods that enable determination of both the exact number of motors participating in motility and their organization on subcellular cargos. Here we present a biosynthetic method that enables exactly two kinesin-1 molecules to be organized on linear scaffolds that separate the motors by a distance of 50 nm.
View Article and Find Full Text PDFA series of [60]fullerene-substituted phenylalanine (Baa) and lysine derivatives have been prepared by the condensation of 1,2-(4'-oxocyclohexano)fullerene with the appropriately protected (4-amino)phenylalanine and lysine, respectively. Conversion of the imine to the corresponding amine is achieved by di-acid catalyzed hydroboration. The reduction of the imine is not accompanied by hydroboration of the fullerene cage.
View Article and Find Full Text PDFWe report the formation of a fullerene-peptide conjugate via the incorporation of a fullerene substituted phenylalanine derivative, "Bucky amino acid" (Baa), to a cationic peptide, which acts as a passport for intracellular delivery, enabling transport of a range of sequences into HEK-293, HepG2, and neuroblastoma cells where the peptides in the absence of the fullerene amino acid cannot enter the cell. Delivery of the fullerene species to either the cytoplasm or nucleus of the cell is demonstrated. Fullerene peptides based on the nuclear localization sequence (NLS), H-Baa-Lys(FITC)-Lys-Lys-Arg-Lys-Val-OH, can actively cross over the cell membrane and accumulate significantly around the nucleus of HEK-293 and neuroblastoma cells, while H-Baa-Lys(FITC)-Lys8-OH accumulates in the cytoplasm.
View Article and Find Full Text PDFThe widespread extinctions of large mammals at the end of the Pleistocene epoch have often been attributed to the depredations of humans; here we present genetic evidence that questions this assumption. We used ancient DNA and Bayesian techniques to reconstruct a detailed genetic history of bison throughout the late Pleistocene and Holocene epochs. Our analyses depict a large diverse population living throughout Beringia until around 37,000 years before the present, when the population's genetic diversity began to decline dramatically.
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