Calvin cycle genes in Nitrobacter vulgaris T3

Abstract The genes encoding the Calvin cycle enzymes of Nitrobacter vulgaris T3 are found as two separate clusters on the chromosome. One cluster contains the genes for the large and small subunits of ribulose-1,5-biphosphate carboxylase/oxygenase (RuBisCO), glyceraldehyde-3-phosphate dehydrogenase, and one encoding a regulatory protein of the LysR family. The other cluster contains the genes for fructose-1,6-/sedoheptulose-1,7-bisphosphatase, phosphoribulokinase, and fructose-1,6-/sedoheptulose-1,7-biphosphate aldolase. With the exception of the LysR-like gene, the genes in each cluster are apparently transcribed in the same direction. The deduced amino acid sequence of both the large and small subunits of RuBisCO are most similar (84–86%) to those of Thiobacillus ferrooxidans and Chromatium vinosum . The deduced sequences of phosphoribulokinase and fructose/sedoheptulose bisphosphatase are 67–73 aand 44–46% similar to those reported for other autotrophic bacteria, respectively.     

Modulation of fibroblast response to maitotoxin along the cell division cycle

Maitotoxin (MTX) induces an increase of [Ca²⁺]_i and of phosphoinositide breakdown in various cell types. The [Ca²⁺]_i increase followed with fluorescent probes on cell suspensions has been described as slow and lasting, in contrast to the signal induced by calcium ionophores such as ionomycin. MTX effects have been studied on two fibroblastic cell lines, BHK21 C13 and FR 3T3, synchronized by serum deprivation treatment performed in an isoleucine-free medium for BHK21 C13 cells. In BHK21 C13 cells, flow cytometry analysis showed that two stages, G1/S and G2/M, were particularly susceptible to MTX treatment. Scanning laser cytometry demonstrated that calcium response of FR 3T3 fibroblasts followed with Indo-1 varied during the cell division cycle. The [Ca²⁺]_i increase was almost always vertical, but its delay after MTX addition lasted from zero (S and G2/M transition) to 10–20 min (G1) or more (G2). No [Ca²⁺]_i change could be detected during mitosis. The [Ca²⁺]_i response at the S phase was biphasic. These observations suggest that (1) the lasting response described in the literature represents a global cell population effect, and (2) cells are more sensitive to MTX at specific stages of the cell division cycle, which could correspond to periods when calcium signals have been detected in different cell types.Abbreviations MTX maitotoxin - [Ca²⁺]_i intracellular calcium concentration - IP₃ inositol triphosphate     

Genetic analysis of human p34CDC2 function in fission yeast

The p34^cdc2 protein kinase plays a key role in the control of the mitotic cell cycle of fission yeast, being required for both entry into S-phase and for entry into mitosis in the mitotic cell cycle, as well as for the initiation of the second meiotic nuclear division. In recent years, structural and functional homologues of p34^cdc2, as well as several of the proteins that interact with and regulate p34^cdc2 function in fission yeast, have been identified in a wide range of higher eukaryotic cell types, suggesting that the control mechanisms uncovered in this simple eukaryote are likely to be well conserved across evolution. Here we describe the construction and characterisation of a fission yeast strain in which the endogenous p34^cdc2 protein is entirely absent and is replaced by its human functional homologue p34^CDC2, We have used this strain to analyse aspects of the function of the human p34^CDC2 protein genetically. We show that the function of the human p34^CDC2 protein in fission yeast cells is dependent upon the action of the protein tyrosine phosphatase p80^cdc25 that it responds to altered levels of both the mitotic inhibitor p107²³³¹ and the p34^cdc2-binding protein p13^suc1, and is lethal in combination with the mutant B-type cyclin p56^cdc13-117. In addition, we demonstrate that the human p34^CDC2 protein is proficient for fission yeast meiosis, and examine the behaviour of two mutant p34^CDC2 proteins in fission yeast.     

Cell cycle dependence of cytotoxicity and clastogenicity induced by treatment of synchronized human diploid fibroblasts with sodium fluoride

To study the cell cycle dependence of cytotoxicity and clastogenicity of sodium fluoride (NaF), synchronized human diploid fibroblasts were treated with NaF during different phases of the cell cycle and analyzed. Exponentially growing cells were synchronized by the following two procedures. (1) The cells were synchronized at G₀/G₁ phase by a period of growth in medium containing 1% serum (low serum medium). (2) The cells were synchronized at the G₁/S boundary by growth in low serum medium, followed by hydroxyurea treatment (Tsutsui et al., 1984a). Synchronized cells were treated with NaF for 3 h during the G₁ phase or G₂ phase, and for each of three 3-h periods during the S phase which lasted 9 h. Cytotoxicity, as determined by a decrease in colony-forming ability, was dependent upon the phase of the cell cycle during which NaF treatment was administered. The highest lethality was induced in when the cultures were treated with NaF during the second or third 3 h of S phase (middle or late S phase, respectively), or G₂ phase. Little lethality was observed in cultures in G₁ phase. Inducibility of chromosome aberrations of the cells following treatment with NaF was also dependent upon the phase of the cell cycle. A significant increase in the incidence of chromosome aberrations was observed only in cultures treated with NaF during early and / or middle S phases of cell cycle. These results suggest that cytotoxicity and clastogenicity of NaF to cultured human diploid fibroblasts are cell cycle dependent, and that the cells in early and middle S phases are more sensitive to the effects.     

Effects of the parasitic botfly Philornis carinatus on nestling house wrens,Troglodytes aedon,in Costa Rica

I studied the life cycle of a botfly (Diptera: Muscidae: Philornis carinatus) and examined the effects of botfly ectoparasitism on nestling house wrens (Passeriformes: Troglodytidae: Troglodytes aedon) during three years in Costa Rica. At three study sites, I found that nestlings were relatively unaffected by botflies, in contrast to all other studies of birds infected with philornid botflies. At Monteverde, the main study site, infected chicks grew slightly slower and had slightly shorter tarsi and wing chords than uninfected chicks, but both groups fledged at similar weights. Since weight at fledging is the only growth character associated with post-fledging survivorship, botfly infections likely cost wrens little in terms of fitness. At all sites, fledging success did not differ between infected and uninfected nests. Botfly infections were more prevalent at two lower elevation sites than at the high elevation Monteverde side. Infection prevalence increased during the nesting season at all study sites, which suggests a botfly life cycle in which adult population levels increase during the wren breeding season and then decline during a dormant period when wrens are not nesting. Finally, botflies may attack chicks throughout the period before fledging, but there is no indication they locate nests before hatching. In sum, botfly parasitism on wrens appears to be benign, perhaps because the study sites are at the edge of the botfly's range or because wrens are not a preferred host.     

Diurnal variations of amino acids and organic acids in xylem fluid from Lagerstroemia indica: an endogenous circadian rhythm

Diurnal variations in the concentrations of major organic compounds occurred in xylem fluid extracted from Lagerstroemia indica L. The concentration of amino acids and the N/C ratio was at a maximum and that of organic acids was at a minimum between 1230 and 2030 h. Since the concentrations of total organic nitrogen, total amino acids and most individual amino acids (but not organic acids or sugars) were also proportional to xylem tension two experiments were performed to discern whether variations in chemistry were a consequence of diurnal changes in moisture stress. In the first experiment, L. indica , exposed to variable levels of moisture stress during midday, manifested an increase in organic acids and a reduction in the N/C ratio. In the second experiment, chemical profiles of xylem fluid were collected and compared for plants exposed to a natural photoperiod, constant darkness or continuous light at noon and midnight. After 1 day amino acids increased in concentration during midday for all treatments; the variation was greatest (10-fold) for plants in constant darkness where xylem tension varied from 0.20 to 0.25 MPa. Only plants exposed to continuous light lost a diurnal rhythm after 3 days. Thus, the circadian rhythm was endogenous, terminated in continuous light and was not mediated by changes in moisture stress. Glutamine accounted for most of the diurnal variation in total amino acids, organic nitrogen and the N/C ratio in xylem fluid.     

Biomass and carbon storage of the North American deciduous forest

Field measures of tree and shrub dimensions were used with established biomass equations in a stratified, two-stage cluster sampling design to estimate above-ground ovendry woody biomass and carbon storage of the eastern deciduous forest of North America. Biomass averaged 8.1 ± 1.4 (95% C.I.) kg/m² and totaled 18.1 ± 3.1 (95% C.I.) gigatons. Carbon storage averaged 3.6 ± 0.6 (95% C.I.) kg/m² and totaled 8.1 ± 1.4 (95% C.I.) gigatons. These values are lower than previous estimates commonly used in the analysis of the global carbon budget which range from 17.1 to 23.1 kg/m² for biomass and 7.7 to 10.4 kg/m² for carbon storage. These new estimates for the deciduous forest, together with earlier work in the boreal forest begin to reveal a pattern of overestimation of global carbon storage by vegetation in analyses of the global carbon budget. We discuss reasons for the differences between the new and earlier estimates, as well as implications for our understanding of the global carbon cycle.     

The 28 kDa apoprotein of CP 26 in PS II binds copper

Photosystem II (PS II) particles isolated from spinach in the presence of 10 M CuSO₄ contained 1.2 copper/300 Chl that was resistant to EDTA. When CuSO₄ was not added during the isolation, PS II particles contained variable amounts of copper resistant to EDTA (0.1–1.1 copper/300 Chl). No correlation was found between copper content and oxygen evolving capacity of the PS II particles. To identify the copper binding protein, we developed a fractionation procedure which included solubilisation of PS II particles followed by precipitation with polyethylene glycol. A 22-fold purification of copper with respect to protein was achieved for a 28 kDa protein. Partial amino acid sequence of a 13 kDa fragment, obtained after V8 (endo Glu-C) protease treatment, showed identity with CP 26 over a 14 amino acid stretch. EPR measurements on the purified protein suggest oxygen and/or nitrogen as ligands for copper but tend to exclude sulfur. We conclude that the 28 kDa apoprotein of CP 26 from spinach binds one copper per molecule of CP 26. A possible function for this copper protein in the xanthophyll cycle is discussed.Abbreviations CP 26 and CP 29 chlorophyll a/b protein complex 26 and 29 - LHC II light-harvesting chlorophyll a/b protein complex of Photosystem II - SB14 sulfobetaine 14 A preliminary report of these results was presented at the IX Int. Congress on Photosynthesis, Nagoya, Japan, 1992.     

MAP kinase kinase: A node connecting multiple pathways

Summry— Numerous studies have been published these last few years on the involvement of MAP kinases in signal transduction reflecting their importance in cell cycle and cell growth controls. The identification and the characterization of their direct upstream activator has considerably enlarged our understanding of the phosphorylation network. The MAP kinase kinases (MAPKKs) are dual-specificity protein kinases which phosphorylate and activate MAP kinases. To date, MAPKK homologues have been found in yeast, invertebrates, amphibians, and mammals. Moreover, the MAPKK/MAPK phosphorylation switch constitutes a basic module activated in distinct pathways in yeast and in vertebrates. MAPKK regulation studies have led to the discovery of at least four MAPKK convergent pathways in higher organisms. One of these is similar to the yeast pheromone response pathway which includes the ste11 protein kinase. Two other pathways require the activation of either one or both of the serine/threonine kinase-encoded oncogenes c-Raf-I and c-Mos. Additionally, recent studies suggest a possible effect of the cell cycle control regulatory cyclin-dependent kinase 1 (cdc2) on MAPKK activity. Finally, MAPKKs seem to be essential transducers through which signals must pass before reaching the nucleus.     

Cell cycle mutation in Paramecium tetraurelia discriminates between sexual and vegetative functions

The temperature-sensitive mutation cc1 blocks a number of cell cycle processes in Paramecium including macronuclear DNA synthesis, oral morphogenesis, and the later stages of micronuclear mitosis. Oral morphogenesis and micronuclear mitosis also occur in the sexual pathway. This study shows that cc1 cells can proceed through conjugation or autogamy under restrictive conditions; neither stomatogenesis nor micronuclear mitosis is blocked. Fertilization and macronuclear determination occur normally, but DNA synthesis in macronuclear anlagen is blocked. Therefore, this mutation discriminates between oral replacement during meiosis and vegetative prefission stomatogenesis, and between mitotic spindle elongation during the pregamic and postzygotic divisions and spindle elongation during the vegetative cell cycle. These results point to a fundamental regulatory difference between morphogenesis in the vegetative and sexual pathways. © 1994 Wiley-Liss, Inc.