Potato virus X: structure, disassembly and reconstitution

This paper summarizes some structural characteristics of Potato virus X (PVX), the flexuous filamentous plant potexvirus. A model of PVX coat protein (CP) tertiary structure in the virion proposed on the basis of tritium planigraphy combined with predictions of the protein tertiary structure is described. A possible role of glycosylation and phosphorylation in the CP structure and function is discussed. Two forms of PVX virion disassembly are discussed: (i) the virion co-translational disassembly after PVX CP in situ phosphorylation and (ii) disassembly of PVX triggered by different factors after linear destabilization of the virion by binding of the PVX-coded movement protein (TGBp1) to one end of the polar CP-helix. Special emphasis was placed on a translational activation of encapsidated PVX RNA and rapid disassembly of TGBp1-PVX complexes into free RNA and CP. The results of experiments on the PVX CP repolymerization and PVX reconstitution are considered. In particular, the products assembled from PVX RNA, CP and TGBp1 were examined. Single-tailed particles were found with a helical, head-like structure consisting of helically arranged CP subunits located at the 5'-tail of RNA; the TGBp1 was bound to the end of the head. Translatable 'RNA-CP-TGBp1' complexes may represent the transport form of the PVX infection.     

Geographic patterns of genetic differentiation and plumage colour variation are different in the pied flycatcher (Ficedula hypoleuca)

The pied flycatcher is one of the most phenotypically variable bird species in Europe. The geographic variation in phenotypes has often been attributed to spatial variation in selection regimes that is associated with the presence or absence of the congeneric collared flycatcher. Spatial variation in phenotypes could however also be generated by spatially restricted gene flow and genetic drift. We examined the genetic population structure of pied flycatchers across the breeding range and applied the phenotypic Q _ST ( P _ST)– F _ST approach to detect indirect signals of divergent selection on dorsal plumage colouration in pied flycatcher males. Allelic frequencies at neutral markers were found to significantly differ among populations breeding in central and southern Europe whereas northerly breeding pied flycatchers were found to be one apparently panmictic group of individuals. Pairwise differences between phenotypic ( P _ST) and neutral genetic distances ( F _ST) were positively correlated after removing the most differentiated Spanish and Swiss populations from the analysis, suggesting that genetic drift may have contributed to the observed phenotypic differentiation in some parts of the pied flycatcher breeding range. Differentiation in dorsal plumage colouration however greatly exceeded that observed at neutral genetic markers, which indicates that the observed pattern of phenotypic differentiation is unlikely to be solely maintained by restricted gene flow and genetic drift.     

Separate Oscillations of the Electrogenic Pump and of a K+ -Channel in Nitella as Revealed by Simultaneous Measurement of Membrane Potential and of Resistance

In Nitella oscillations of membrane potential with periods ofabout 15 min and of about 1 h can be observed. The comparisonof the related changes in resistance and in potential showsthat the 1-h oscillation controls a carrier-type transporter,probably an electrogenic pump with a stoichiometry of 1 H⁺/1ATP. The control loop related to the 1-h oscillation can bestimulated by internal pH as changed by butyrate or procaine.IV-curve studies show that the 15-min oscillation modulatesthe conductivity of a K⁺ -channel. No way has been found toinfluence the spontaneously occurring 15-min oscillation whichprobably is generated in the chioroplasts. The oscillationsseem to provide a means of exerting a selective influence onone transporter. Correspondence to: Institut für Angewandte Physik, NeueUniversität, Haus N61A, D-2300 Kiel, F.R.G. Key words: H⁺-pump, IV-curves, Nitella, oscillations, pH-regulation, potassium channel, stoichiometry