Fluoride, when incorporated in the apatite, stabilizes the structure. The purpose of this study was to determine the consequences of fluoride (F) substitution on the physico-chemical properties of apatites. F-containing apatites were prepared by precipitation or by hydrolysis of CaHPO4 in solutions containing different F concentrations and characterized using x-ray diffraction, FT-IR spectroscopy, scanning electron microscopy, thermogravimetry and chemical analyses. Results showed that F incorporation have the following effects: (a) decrease in a-axis dimension, (b) increase in crystal size and thickness, (c) decrease in calcium deficiency, and (d) lower solubility.

As part of the Synthetic Yeast 2.0 (Sc2.0) project, we designed and synthesized synthetic chromosome I. The total length of synI is ~21.4% shorter than wild-type chromosome I, the smallest chromosome in Saccharomyces cerevisiae. SynI was designed for attachment to another synthetic chromosome due to concerns of potential instability and karyotype imbalance. We used a variation of a previously developed, robust CRISPR-Cas9 method to fuse chromosome I to other chromosome arms of varying length: chrIXR (84 kb), chrIIIR (202 kb) and chrIVR (1 Mb). All fusion chromosome strains grew like wild-type so we decided to attach synI to synIII. Through the investigation of three-dimensional structures of fusion chromosome strains, unexpected loops and twisted structures were formed in chrIII-I and chrIX-III-I fusion chromosomes, which depend on silencing proteinSir3. These results suggest a previously unappreciated 3D interaction between HMR and the adjacent telomere. We used these fusion chromosomes to show that axial element Red1 binding in meiosis is not strictly chromosome size dependent even though Red1 binding is enriched on the three smallest chromosomes in wild-type yeast, and we discovered an unexpected role for centromeres in Red1 binding patterns.

SummaryMeiotic chromosomes organize around a cohesin-dependent axial element, which promotes meiotic recombination and fertility. In the absence of cohesin, axial-element proteins instead accumulate in poorly understood genomic regions. Here, we show in S. cerevisiae that these regions are particularly enriched for axis proteins even on wild-type chromosomes and thus reflect a cohesin-independent recruitment mechanism. By contrast, other organizers of chromosome structure, including cohesin, condensin, and topoisomerases, are depleted from the same regions. This spatial patterning is observable before meiotic entry and therefore independent of meiotic recombination. Indeed, the regional density of gene-coding sequences is sufficient to predict a large fraction of cohesin-independent axis protein binding, suggesting that the gene-associated chromatin landscape plays a role in modulating axis protein deposition. The increased accumulation of axis proteins in these regions corresponds to a greater potential for initiation of recombination and progression to crossovers.