Kinetochores are the proteinaceous complexes that assemble on centromeric DNA and direct eukaryotic chromosome segregation. The mechanisms by which higher eukaryotic cells define centromeres are poorly understood. Possible molecular contributors to centromere specification include the underlying DNA sequences and epigenetic factors such as binding of the centromeric histone centromere protein A (CENP-A). Frog egg extracts are an attractive system for studying centromere definition and kinetochore assembly. To facilitate such studies, we cloned a Xenopus laevis homologue of CENP-A (XCENP-A). We identified centromere-associated DNA sequences by cloning fragments of DNA that copurified with XCENP-A by chromatin immunoprecipitation. XCENP-A associates with frog centromeric repeat 1 (Fcr1), a 174-base pair repeat containing a possible CENP-B box. Southern blots of partially digested genomic DNA revealed large ordered arrays of Fcr1 in the genome. Fluorescent in situ hybridization with Fcr1 probes stained most centromeres in cultured cells. By staining lampbrush chromosomes, we specifically identified the 11 (of 18) chromosomes that stain consistently with Fcr1 probes.

Refinement of the class A I B II C V materials continue as a candidate for solid-state neutron detectors. Such a device would have greater efficiency, in a compact form, than present day gasfilled 3 He and 10 BF 3 detectors. The 6 Li(n,t) 4 He reaction yields a total Q value of 4.78 MeV, larger than 10 B, and easily identified above background radiations. Hence, devices composed of either natural Li (nominally 7.5% 6 Li) or enriched 6 Li (usually 95% 6 Li) may provide a semiconductor material for compact high efficiency neutron detectors. A sub-branch of the III-V semiconductors, the filled tetrahedral compounds, A I B II C V , known as Nowotny-Juza compounds, are known for their desirable cubic crystal structure. Starting material was synthesized by equimolar portions of Li, Zn, and As sealed under vacuum (10-6 Torr) in quartz ampoules with a boron nitride lining, and reacted in a compounding furnace [1]. The synthesized material showed signs of high impurity levels from material and electrical property characterization. In the present work, a static vacuum sublimation of synthesized LiZnAs loaded in a quartz vessel was performed to help purify the synthesized material. The chemical composition of the sublimed material and remains material was confirmed by Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). Lithium was not detected in the sublimed material, however, near stoichiometric amounts of each constituent element were found in the remains material for LiZnAs. X-ray diffraction phase identification scans of the remains material and sublimed material were compared, and further indicated the impurity materials were removed from the synthesized materials. The remaining powder post the sublimation process showed characteristics of a higher purity ternary compound.

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