Etude du métabolisme d'une substance affectant la coagulation sanguine par la méthode des indicateurs radioactifs

Summary Radioactive 2-bromo-3-hydroxy-1:4-naphtoquinone has been used for the exploration of the metabolism of substances which influence the course of blood-clotting. It has been found that this substance diffuses very rapidly into the blood, and that the liver is not characterized by any elective fixation-power.     

Aquatic vertebrate assemblages of the Upper Clear Creek Watershed, California

We sampled streams in the Upper Clear Creek Watershed in northwestern California in fall 2004 and fall 2005 to document assemblages of aquatic vertebrates and to provide resource managers with information on the importance of these assemblages in terms of regional biodiversity. We used single-pass backpack electrofishing to sample 15 sites in fall 2004 and the same 15 sites plus 4 new sites in fall 2005. We captured 10 fish taxa and 2 species of larval amphibians. Seven of the fish taxa were native species. Of the exotic species, only brook trout ( Salvelinus fontinalis ) occurred at more than 1 site. Ordinations by nonmetric multidimensional scaling indicated a gradient from sites with rainbow trout ( Oncorhynchus mykiss ), Pacific giant salamander ( Dicamptodon tenebrosus ), and tailed frog ( Ascaphus truei ) to sites dominated by riffle sculpin ( Cottus gulosus ), California roach ( Hesperoleucas symmetricus ), and Sacramento sucker ( Catostomus occidentalis ). The gradient in species composition was associated with changes in elevation, gradient, discharge, and substrate. The Upper Clear Creek Watershed represents a unique area of overlap between the North Coast California amphibian fauna and the Central Valley fish fauna with a notable paucity of exotic fishes and amphibians. Preservation of the integrity of native aquatic assemblages is an important goal for aquatic resource management in the region; our results provide a critcial baseline to gauge future management actions.     

番木瓜环斑病毒复制酶基因的克隆和序列分析

用ＲＴ－ＰＣＲ技术从ＰＲＶ－ＡＬ中分离到复制酶（ＲＰ）基因，将基因克隆进载体ｐＵＣ１８，用双脱氧链终止法测定了基因序列，表明其全长为１６０２ｂｐ，与国内外报道的ＨＡ５－１、ＹＫ和Ｓｍ的ＲＰ基因相比，同源性分别达８２．８０％，９５．０７％和９１．８３％．     

Intense and highly localized gene conversion activity in human meiotic crossover hot spots

Meiotic gene conversion has an important role in allele diversification and in the homogenization of gene and other repeat DNA sequence families, sometimes with pathological consequences. But little is known about the dynamics of gene conversion in humans and its relationship to meiotic crossover. We therefore developed screening and selection methods to characterize sperm conversions in two meiotic crossover hot spots in the major histocompatibility complex (MHC) and one in the sex chromosomal pseudoautosomal pairing region PAR1 (ref. 9). All three hot spots are active in gene conversion and crossover. Conversion tracts are short and define a steep bidirectional gradient centered at the peak of crossover activity, consistent with crossovers and conversions being produced by the same recombination-initiating events. These initiations seem to be spread over a narrow zone, rather than occurring at a single site, and seem preferentially to yield conversions rather than crossovers. Crossover breakpoints are more broadly diffused than conversion breakpoints, suggesting either differences between conversion and crossover processing after initiation or the existence of a quality control checkpoint at which short interactions between homologous chromosomes are preferentially aborted as conversions.