Location of Template on the Human Ribosome as Revealed from Data on Cross-Linking with Reactive mRNA Analogs

In this review we summarize data on the location of template on the human ribosome that we obtained from cross-linking (affinity labeling) experiments using reactive mRNA analogs. Types of mRNA analogs, model complexes of these analogs with 80S ribosomes, and methods for analysis of the ribosomal components (proteins and rRNA nucleotides) cross-linked with the mRNA analogs are reviewed. From analysis of the cross-linking data, we suggest a scheme for the arrangement of mRNA on the human ribosome and compare the organization of the mRNA binding center on human and Escherichia coli ribosomes.     

Trapping, loss and annihilation of excitations in a photosynthetic system: II. Experiments with the purple bacteria Rhodospirillum rubrum and Rhodopseudomonas capsulata

In this paper a number of experiments with the purple bacteria Rhodospirillum rubrum and Rhodopseudomonas capsulata is described in which the total fluorescence yield and/or the total fraction of reaction centers closed after a picosecond laser pulse were measured as a function of the pulse intensity. The conditions were such that the reaction centers were either all in the open or all in the closed state before the pulse arrived. These experiments are analysed using the theoretical formalism discussed in the preceding paper (Den Hollander, W.T.F., Bakker J.G.C., and Van Grondelle, R., Biochim. Biophys. Acta 725, 492–507). From the experimental results the number of connected photosynthetic units, λ, the rate of energy transfer between neighboring antenna molecules, k_h, and the rate of trapping by an open reaction center, k^o_t, can be estimated. For R. rubrum it is found that λ = 14−17, k_h = (1−2)·10¹² s⁻¹ and k^o_t = (4−6)·10¹¹ s⁻¹, for Rps. capsulata λ ≈ 30, k_h ≈ 4·10¹¹ s⁻¹ and k^o_t ≈ 3·10¹¹ s⁻¹. The findings are discussed in terms of current models for the structure of the antenna and the kinetic properties of the decay processes occurring in these purple bacteria.     

MTOCs in higher plant cells: an immunofluorescent study of microtubule assembly sites following depolymerization by APM

Summary A one hour exposure to 3 M amiprophos-methyl (APM) depolymerizes all MT arrays in cells from higher plant suspension cultures. On removal of APM, MT repolymerization sites are detected using immunofluorescent staining. During interphase, Mt arrays return uniformly dispersed across the cell cortex with transverse arrays in elongated cells and random arrays in isodiametric cells. During cell division, MT arrays return as follows: Prophase-MT arrays return in association with the nuclear envelope. Metaphase-MTs return associated with chromosomes. Teleophase-MTs return in apparent association with the reforming nuclear envelope and as aberrant phragmoplasts. MTOCs in higher plant cells may be membrane associated at many stages in the cell cycle. Isolated, condensed chromosomes are capable of nucleating MTs, which can attain small, spindle-like configurations.Abbreviations APM Amiprophos-methyl - MT Microtubule - MTOC Microtubule organizing center - NS Nucleating site     

Floristics and plant biogeography in China

In 1998, a revolutionary system of angiosperm classification, the Angiosperm Phylogeny Group system was published.Meanwhile, another new system of classification of angiosperms, the eight-class system was proposed by C.Y. Wu and colleagues based on long term work on the flora of China. The Flora Reipublicae Popularis Sinicae project was initiated in 1959 and completed by 2004. It is the largest Flora so far completed in the world, including 31 228 species of vascular plants,or one-eighth of the global plant diversity. The English-language and updated Flora of China (FOC) is an international joint effort initiated in 1988 and accelerated in 1998. Up to now, 15 of the 24 volumes of the FOC have been published. Based on the fioristic data, the composition, characteristics, floristic divisions and affinities of the flora of China have been studied by Wu and colleagues since 1965. In the past 10years, analyses of the available floristic data have been very productive.The East Asiatic Floristic Kingdom was proposed in 1998. All 346 families of angiosperms in China, according to the eightclass system of classification, were comprehensively discussed by using knowledge of current and historical distribution of seed plants in the world, together with some morphological and molecular data. A scheme of distribution patterns or areal-types of families and genera of seed plants in China was modified and elucidated, together with a proposed scheme of areal-types of the world. Molecular phylogenetic and biogeographical studies of angiosperms in China in the past 10 yearsalso witnessed a progressive development. Integration of morphological and molecular data and fossil evidence revealed some significant results. Eastern Asia, which used to be regarded as an important center of survival during the ice age, is likely an important center of diversification of angiosperms.     

Halothane Increases Non-vesicular [<Superscript>3</Superscript>H]dopamine Release from Brain Cortical Slices

Experimental data suggest that halothane anesthesia is associated with significant changes in dopamine (DA) concentration in some brain regions but the mechanism of this effect is not well known. Rat brain cortical slices were labeled with [³H]DA to further characterize the effects of halothane on the release of this neurotransmitter from the central nervous system. Halothane induced an increase on the release of [³H]DA that was dependent on incubation time and anesthetic concentration (0.012, 0.024, 0.048, 0.072 and 0.096 mM). This effect was independent of extracellular or intracellular calcium. In addition, [³H]DA release evoked by halothane was not affected by TTX (blocker of voltage-dependent Na⁺ channels) or reserpine (a blocker of vesicular monoamine transporter). These data suggest that [³H]DA release induced by halothane is non-vesicular and would be mediated by the dopamine transporter (DAT) and norepinephrine transporter (NET). GBR 12909 and nomifensine, inhibitors of DAT, decreased the release of [³H]DA evoked by halothane. Nisoxetine, a blocker of NET, reduced the release of [³H]DA induced by halothane. In addition, GBR 12909, nisoxetine and, halothane decrease the uptake of [³H]DA into rat brain cortical slices. A decrease on halothane-induced release of [³H]DA was also observed when the brain cortical slices were incubated at low temperature and low extracellular sodium, which are known to interfere with the carrier-mediated release of the neurotransmitter. Ouabain, a Na⁺/K⁺ ATPase pump inhibitor, which induces DA release through reverse transport, decreased [³H]DA release induced by halothane. It is suggested that halothane increases [³H]DA release in brain cortical slices that is mediated by DAT and NET present in the plasma membrane.     

3D structure of bovine pancreatic ribonuclease A in aqueous solution: An approach to tertiary structure determination from a small basis of1H NMR NOE correlations

Summary A method is proposed to generate initial structures in cases where the distance geometry method may fail, such as when the set of¹H NMR NOE-based distance constraints is small in relation to the size of the protein. The method introduces an initial correlation between the and backbone angles (based on empirical observations) which is relaxed in later stages of the calculation. The obtained initial structures are refined by well-established methods of energy minimization and restrained molecular dynamics. The method is applied to determine the solution structure of Ribonuclease A (124 residues) from a NOE basis consisting of 467 NOE cross-correlations (97 intra-residue, 206 sequential, 23 medium-range and 141 long-range) obtained at 360 MHz. The global shape and backbone overall fold of the eight final refined structures are close to those shown by the crystal structure. A meaningful difference in the positioning of the catalytically important His¹¹⁹ side chain in the solution and crystal structures has been detected.     

The general occurrence of “plastid initials” and their development into plastids in cortical cells of woody plants in winter

Summary Electron microscopic studies revealed that plastid initials, presumed precursors of plastids, occur in cortical cells of the following plants studied in February and March: Betula ermanii Cham.; Prunus sargentii Rhed.; Pyrus communis L.; Ribes sinanense F. Maekawa; Salix matsudana Koidz. forma tortuosa Rhed.; and Sambucus sieboldiana var. miquelii Hara. Since plastid initials were found previously in Malus pumila Mill., Morus bombycis Koidz. and Populus euramericana cv. gelrica (Sagisaka 1991), plastid initials have been found in all woody plants examined to date. In P. euramericana cv. gelrica, at later stages of the development of the initials in March, the conglomerates of plastid initials became heterogeneous in terms of size, extent of thylakoid formation and ability to form starch granules. The formation of prolamellar structures was frequently observed in cells of Magnolia kobus var. borealis Sarg., which was sampled on April 19. These observations suggest the course of events in the development of the plastid initial and the continuity of the life of amyloplasts over a year in the life of woody plants.     

What governs the reaction center excitation wavelength of photosystems I and II?

The sun’s spectrum harvested through photosynthesis is the primary source of energy for life on earth. Plants, green algae, and cyanobacteria—the major primary producers on earth—utilize reaction centers that operate at wavelengths of 680 and 700 nm. Why were these wavelengths “chosen” in evolution? This study analyzes the efficiency of light conversion into chemical energy as a function of hypothetical reaction center absorption wavelengths given the sun’s spectrum and the overpotential cost associated with charge separation. Surprisingly, it is found here that when taking into account the empirical charge separation cost the range 680–720 nm maximizes the conversion efficiency. This suggests the possibility that the wavelengths of photosystem I and II were optimized at some point in their evolution for the maximal utilization of the sun’s spectrum.     

Binding of Plasma Membrane Lipids Recruits the Yeast Integral Membrane Protein Ist2 to the Cortical ER

Recruitment of cytosolic proteins to individual membranes is governed by a combination of protein–protein and protein–membrane interactions. Many proteins recognize phosphatidylinositol 4,5-bisphosphate [PI(4,5)P₂] at the cytosolic surface of the plasma membrane (PM). Here, we show that a protein–lipid interaction can also serve as a dominant signal for the sorting of integral membrane proteins. Interaction with phosphatidly-inositolphosphates (PIPs) at the PM is involved in the targeting of the polytopic yeast protein Ist2 to PM-associated domains of the cortical endoplasmic reticulum (ER). Moreover, binding of PI(4,5)P₂ at the PM functions as a dominant mechanism that targets other integral membrane proteins to PM-associated domains of the cortical ER. This sorting to a subdomain of the ER abolishes proteasomal degradation and trafficking along the classical secretory (sec) pathway. In combination with the localization of IST2 mRNA to the bud tip and other redundant signals in Ist2, binding of PIPs leads to efficient accumulation of Ist2 at domains of the cortical ER from where the protein may reach the PM independently of the function of the sec-pathway.