Repeat-based holocentromeres influence genome architecture and karyotype evolution.

The centromere represents a single region in most eukaryotic chromosomes. However, several plant and animal lineages assemble holocentromeres along the entire chromosome length. Here, we compare genome organization and evolution as a function of centromere type by assembling chromosome-scale holocentric genomes with repeat-based holocentromeres from three beak-sedge (Rhynchospora pubera, R.

Complex sequence organization of heterochromatin in the holocentric plant elucidated by the computational analysis of nanopore reads.

Repeat-rich regions of higher plant genomes are usually associated with constitutive heterochromatin, a specific type of chromatin that forms tightly packed nuclear chromocenters and chromosome bands. There is a large body of cytogenetic evidence that these chromosome regions are often composed of tandemly organized satellite DNA. However, comparatively little is known about the sequence arrangement within heterochromatic regions, which are difficult to assemble due to their repeated nature.

Characterization of repeat arrays in ultra-long nanopore reads reveals frequent origin of satellite DNA from retrotransposon-derived tandem repeats.

Amplification of monomer sequences into long contiguous arrays is the main feature distinguishing satellite DNA from other tandem repeats, yet it is also the main obstacle in its investigation because these arrays are in principle difficult to assemble. Here we explore an alternative, assembly-free approach that utilizes ultra-long Oxford Nanopore reads to infer the length distribution of satellite repeat arrays, their association with other repeats and the prevailing sequence periodicities. Using the satellite DNA-rich legume plant Lathyrus sativus as a model, we demonstrated this approach by analyzing 11 major satellite repeats using a set of nanopore reads ranging from 30 to over 200 kb in length and representing 0.

Photoelectric emission from the alkali metal doped vacuum-ice interface.

The photoelectron photoemission spectra and thresholds for low coverages of Li and K adsorbed on water-ice have been measured, compared with photoionization spectra of the gas-phase atoms, and modeled by quantum chemical calculations. For both alkali metals the threshold for photoemission is dramatically decreased and the cross section increased on adsorption to the water-ice surface. Quantum chemical calculations suggest that the initial state is formed by the metal atoms adsorbed into the water-ice surface, forming a state with a delocalized electron distribution.

A kinetic study of Ca-containing ions reacting with O, O2, CO2 and H2O: implications for calcium ion chemistry in the upper atmosphere.

A series of gas-phase reactions involving molecular Ca-containing ions was studied by the pulsed laser ablation of a calcite target to produce Ca+ in a fast flow of He, followed by the addition of reagents downstream and detection of ions by quadrupole mass spectrometry. Most of the reactions that were studied are important for describing the chemistry of meteor-ablated calcium in the earth's upper atmosphere. The following rate coefficients were measured: k(CaO+ + O --> Ca+ + O2) = (4.