How to halve ploidy: lessons from budding yeast meiosis

Maintenance of ploidy in sexually reproducing organisms requires a specialized form of cell division called meiosis that generates genetically diverse haploid gametes from diploid germ cells. Meiotic cells halve their ploidy by undergoing two rounds of nuclear division (meiosis I and II) after a single round of DNA replication. Research in Saccharomyces cerevisiae (budding yeast) has shown that four major deviations from the mitotic cell cycle during meiosis are essential for halving ploidy. The deviations are (1) formation of a link between homologous chromosomes by crossover, (2) monopolar attachment of sister kinetochores during meiosis I, (3) protection of centromeric cohesion during meiosis I, and (4) suppression of DNA replication following exit from meiosis I. In this review we present the current understanding of the above four processes in budding yeast and examine the possible conservation of molecular mechanisms from yeast to humans.     

A YAC-based physical map of the mouse genome.

A physical map of the mouse genome is an essential tool for both positional cloning and genomic sequencing in this key model system for biomedical research. Indeed, the construction of a mouse physical map with markers spaced at an average interval of 300 kb is one of the stated goals of the Human Genome Project. Here we report the results of a project at the Whitehead Institute/MIT Center for Genome Research to construct such a physical map of the mouse. We built the map by screening sequenced-tagged sites (STSs) against a large-insert yeast artificial chromosome (YAC) library and then integrating the STS-content information with a dense genetic map. The integrated map shows the location of 9,787 loci, providing landmarks with an average spacing of approximately 300 kb and affording YAC coverage of approximately 92% of the mouse genome. We also report the results of a project at the MRC UK Mouse Genome Centre targeted at chromosome X. The project produced a YAC-based map containing 619 loci (with 121 loci in common with the Whitehead map and 498 additional loci), providing especially dense coverage of this sex chromosome. The YAC-based physical map directly facilitates positional cloning of mouse mutations by providing ready access to most of the genome. More generally, use of this map in addition to a newly constructed radiation hybrid (RH) map provides a comprehensive framework for mouse genomic studies.     

Separation of metal ions on inorganic ion-exchange papers

Zusammenfassung Mit anorganischen Ionenaustauchern Titanwolframat und -molybdat imprägnierte Papiere wurden zur Chromatographie mehrerer Metallionen in verschiedenen wässrigen, nichtwässrigen und gemischten Lösungsmitteln verwendet. Trennungen einer Anzahl von ternären und binären Gemischen wurden damit erzielt.     

Effect of chronic alloxan diabetes and insulin treatment on adipose tissue lipid composition of rats

Summary Decreased content of the adipose tissue lipids was observed in chronic alloxan diabetic rats and was restored to normal with insulin treatment. Prolonged insulin treatment in normal rats also resulted in increase of the lipid content of the adipose tissue.     

Effect of cyproterone acetate on the testis and epididymis of the lizard,Psammophilus dorsalis (Gray)

Summary The effect of cyproterone acetate (CPA) on the testis and epididymis of the lizard,Psammophilus dorsalis has been studied. Treatment with CPA affects spermatogenesis and steroid metabolism in the testis. It also causes regression of the epididymis and a decrease in steroidogenic enzyme activity.Acknowledgments. We wish to thank Prof. M.R. Rajasekarasetty for his encouragement, Dr K.V. Rao, Nagpur, for a generous gift of cyproterone acetate, Dr V.B. Nadkarni, Dharwar, for permitting the use of his cryostat, Sri B.M. Sekharappa for his technical assistance and UGC, New Delhi for their financial help to one of us (GRS).     

Domainal evolution of a prokaryotic DNA repair protein and its relationship to active-transport proteins

The ABC excision nuclease of Escherichia coli is an ATP-dependent DNA repair enzyme composed of three protein subunits, UvrA, UvrB and UvrC. The DNA sequences of all three genes have been reported. UvrA, the component that binds directly to the DNA, and UvrB, which attaches itself to the UvrA-DNA complex, both contain consensus sequences though to be diagnostic of ATP-binding sites, although the UvrC sequence does not. We now report that a computer analysis of the UvrA sequence has revealed an unusual series of internal duplications centering around putative metal-binding sites which may be involved in the interaction with DNA. We also find a strong evolutionary relationship to a family of prokaryotic membrane-associated active-transport proteins.     

Thin layer chromatography of metal ions on a new synthetic inorganic ion-exchanger

Zusammenfassung Neues, für die Trennung anorganischer Ionen nützliches Trägermaterial für Dünnschichtchromatographie.

---

---

The authors are thankful to Dr.S. M. Gulabi, Head, Chemistry Department, for providing research facilities.