Mechanical model of the nucleosome and chromatin

A theoretical framework for evaluating the approximate energy and dynamic properties associated with the folding of DNA into nucleosomes and chromatin is presented. Experimentally determined elastic constants of linear DNA and a simple fold geometry are assumed in order to derive elastic constants for extended and condensed chromatin. The model predicts the Young s modulus of extended and condensed chromatin to within an order of magnitude of experimentally determined values. Thus we demonstrate that the elastic properties of DNA are a primary determinant of the elastic properties of the higher order folded states. The derived elastic constants are used to predict the speed of propagation of small amplitude waves that excite an extension(sound), twist, bend or shear motion in each folded state. Taken together the results demonstrate that folding creates a hierarchy of time, length and energy scales.     

Synthesis of polyglycerol phosphate by Bacillus stearothermophilus.

A particulate enzyme preparation from Bacillus stearothermophilus synthesized 1,3-poly(glycerol phosphage) from CDPglycerol at an optimum pH of 8.0 and the reaction was stimulated by divalent cations. Km for CDPglycerol was 0.18 mM. The synthesis was inhibited by CMP, CDP, and CTP and by concentrations of CDP-glycerol above 0.49 mM. The reaction was irreversible, The product had an average chain length of 8 glycerol units. About two thirds of the polymers were synthesized in entirety while the ramainder were attached to some acceptor by their phosphate end. The enzome was able to synthesize only a limited amount of polymer.     

Dynamic compression counteracts IL-1β induced inducible nitric oxide synthase and cyclo-oxygenase-2 expression in chondrocyte/agarose constructs

Background  

Nitric oxide and prostaglandin E₂ (PGE₂play pivotal roles in both the pathogenesis of osteoarthritis and catabolic processes in articular cartilage. These mediators are influenced by both IL-1β and mechanical loading, and involve alterations in the inducible nitric oxide synthase (iNOS) and cyclo-oxygenase (COX)-2 enzymes. To identify the specific interactions that are activated by both types of stimuli, we examined the effects of dynamic compression on levels of expression of iNOS and COX-2 and involvement of the p38 mitogen-activated protein kinase (MAPK) pathway.     

文山松毛虫质型多角体病毒形态结构及理化性质的研究

对文山松毛虫质型多角体病毒的形态结构及理化特性进行了研究,多角体大部分为六边形,少数为四边形及近园形,其大小在0.47～2.45μ之间,平均为1.1μ。病毒粒子呈球形,无囊膜,致密的核芯区由一层外壳包裹,直径为60nm。病毒粒子表面有12个刺突,放大图象可见其亚单位排列。多角体蛋白的主要成分为一种,分子量为26200道尔顿,多角体蛋白氨基酸组成中不含半胱氨酸;其碱性氨基酸与酸性氨基酸之比为1:2.16。病毒粒子结构蛋白含五条多肽组分。用SDS-热酚法提取所得核酸,其热变性紫外吸收OD_(260)值增加51.6％。抗核酸酶S_1。Tm值为86℃。在1％琼脂糖凝胶电泳中可分为9个片段,而在5％PAGE中,则可分为10个片段。各片段大小在0.66×10~6～2.85×10~6道尔顿之间,总分子量为15.35×10~6。电镜分析研究显示了CPV RNA在0.4μ、0.8μ和1.2μ处有三个分布峰。     

An Investigation into the Rate and Control of Assimilate Movement from Leaves in Pisum sativum

Export studies were made on leaves of Pisum by monitoring the¹⁴CO₂-treated source leaf at its surface at frequent intervals.Radiocarbon levels of fresh leaf samples showed a good correlationwith results from the more conventional methods of radiocarbonestimation which involve destructive analysis. The rate of export was highest in plants which had been defoliated,except for the source leaf 20 h or more before the start ofthe export study. Removal of the shoot apex reduced export andprogressive reduction in sink capacity was associated with decreasedexport rates, particularly over short time periods. Export rateswere similar in defoliated and non-defoliated plants where theshoot apex and the roots had been excised. This suggested thata decrease in the source resulted in higher export rates fromthe remaining source only when active sinks were present; thisin turn suggests that, at least under these conditions, activeremoval of photosynthate is more important in controlling exportthan the photosynthate build-up in the leaf itself. The non-destructive technique enabled comparisons to be madebetween export curves for individual plants. It was found thatin experiments replicated in time, the same relationship betweentreatments was present on different days and the shape of theexport curves was similar but the absolute values for exportedradiocarbon sometimes varied considerably.     

Chilling-induced Lipid Hydrolysis in the Oil Palm (Elaeis guineensis) Mesocarp

Oil palm fruits exposed to temperatures of 15 °C and belowshowed a significant increase in free fatty acid (FFA) contentin the mesocarp. This effect was most pronounced in fruits exposedto 5 °C when FFA levels exceeding 70% of the total oil wereobserved. The increase in FFA was accompanied by an increasein lipid-soluble phosphorus levels and a decrease in carotenecontent. Chilling did not have an effect on palm kernel oil.The results suggest the activation of a lipase in the mesocarpby low temperature stress. Key words: Lipase, oil palm, free fatty acid