The structural and mechanistic basis for recycling of Rab proteins between membrane compartments

Rab proteins are members of the Ras superfamily of GTPases and are key regulators of intracellular vesicular transport. They undergo a cycle of GTPase activity, and this activity is interconnected to a cycle of reversible attachment to membranes. This cycle is mediated by geranylgeranylation of (usually) two C-terminal cysteines, which in turn is effected by Rab geranylgeranyltransferase in concert with REP (Rab escort protein). After delivery to their respective membranes, Rabs are activated by replacement of GDP by GTP, allowing interaction with a wide variety of effector molecules involved in vesicular transport, in particular with docking of transport vesicles to their specific target membranes. After completion of these events and GTP hydrolysis, Rabs are retrieved by GDI (GDP dissociation inhibitor) and delivered to their starting compartment. Here, the structural and mechanistic basis of events occurring in Rab delivery and cycling, and the differences between REP and GDI are discussed on the basis of recent advances in the field.Received 4 November 2004; received after revision 14 February 2005; accepted 31 March 2005     

上海地区不同植物根际荧光假单胞菌多样性

荧光假单胞菌是一种常见的植物根际促生细菌,有开发作为生物农药的潜质．以分离自上海周边地区12种植物根际的104株荧光假单胞菌为研究对象,进行了表型分类,并采用16S—rDNARFLP和REP—PCR技术,系统地研究了荧光假单胞菌的遗传多样性．结果表明：16S—rDNARFLP酶切图谱聚类分析在85％相似性水平上,可将供试菌株划分为9群;REP—PCR指纹图谱聚类分析在76％相似性水平上,可将供试菌株划分为26群,说明上海地区的荧光假单胞菌具有丰富的遗传多样性;聚类分析结果还显示出菌株间亲缘关系与其分离地和所在植物具有相关性,表明环境条件对荧光假单胞菌的发育和遗传分化有重要影响．