Molecular cloning and analysis of genes for production of K5, K7, K12, and K92 capsular polysaccharides in Escherichia coli.

With a DNA fragment from within the region encoding the transport functions for K1 production as a hybridization probe in Southern blot experiments, homologous DNA sequences were detected in the DNA from Escherichia coli strains producing K5, K7, K92, and K100 capsular polysaccharides. No homology with the laboratory strain LE392 was detected. The same DNA probe was used to prescreen cosmid libraries in LE392 by colony hybridization, as a rapid method to isolate clones encoding the genes for K5, K7, K12, and K92 antigen production. Clones carrying sequences homologous to the probe that also produced capsular material were identified by using polyclonal and monoclonal antibodies raised against the K antigen in question and K antigen-specific phages. By restriction enzyme mapping of the appropriate cosmid clones it was possible to align the genes for the production of different K antigens in terms of common restriction endonuclease cleavage sites. A DNA fragment encoding the postulated transport functions for K7 antigen production could complement deletion mutations in the transport functions for K1 antigen production. Thus the transport to the cell surface of chemically distinct polysaccharides may be by a common process. Analysis in E. coli of the proteins produced by plasmids carrying the likely transport functions for K1, K5, and K7 antigen production revealed that each region coded for a similar polypeptide.     

MjK1, a K+ channel from M. jannaschii,mediates K+ uptake and K+ sensitivity in E. coli

The methanogenic and hyperthermophilic deep-sea archaeon Methanococcus jannaschii has three putative K+ channels, MVP (Mj0139), MjK1 (Mj0138.1) and MjK2 (Mj1357). The physiological function of these K+ channels was examined in a viability assay, using the Escherichia coli mutant LB2003 (kup1, DeltakdpABC5, DeltatrkA). While MjK2 expression had no effects on the potassium-dependent phenotype of LB2003, MVP and MjK1 complemented the deficiency at a concentration of 1 mM KCl. In contrast to KcsA, MthK and MVP, MjK1 strongly affected host cell viability at 10 and 100 mM KCl. The toxic effects were less pronounced when growth media were supplemented with the K+ channel blocker BaCl2.     

Mengel, K. and Kirkby, E. A. Principles of plant nutrition

That this text book is now in its fifth edition clearly showsthe strength of its content and presentation, and its relevanceto the scientific community, which should include all thoseinterested in plants and their growth. There are 20 chapters.The first is an overview of definitions and processes whichare considered in much greater depth later. Then follow substantialchapters on ‘The Soil as a Plant Nutrient Medium’,     

陈克恢——国际著名药理学家

编者按 陈克恢 (K.K.Chen) 教授是著名药理学家,是中国药理学的先驱者,他以从中药麻黄中提取分离出止喘有效成分麻黄碱而闻名于世.他移居美国,为美国药理学的发展和新药研发也作出了重要贡献.丁光生教授撰写此文,弥补了陈教授生前未能有机会为本刊撰写刊头专文的遗憾.