Photoaffinity cross-linking of F1ATPase from spinach chloroplasts by 3''-arylazido-β-alanyl-8-azido ATP

UV irradiation of the ATPase (CF₁) from spinach chloroplasts in the presence of 3'-arylazido-β-alanyl-8-azido ATP (8,3'-DiN₃ATP) results in a nucleotide-dependent inactivation of the enzyme and in a nucleotide-dependent formation of -β cross-links. The results demonstrate an interfacial localization of the nucleotide binding sites on CF₁.     

Analysis of peptides from known proteins: Clusterization in sequence space

A combinatorial sequence space (CSS) model was introduced to represent sequences as a set of overlapping k-tuples of some fixed length which correspond to points in the CSS. The aim was to analyze clusterization of protein sequences in the CSS and to test various hypotheses about the possible evolutionary basis of this clusterization. The authors developed an easy-to-use technique which can reveal and analyze such a clusterization in a multidimensional CSS. Application of the technique led to an unexpectedly high clusterization of points in the CSS corresponding to k-tuples from known proteins. The clusterization could not be inferred from nonuniform amino acid frequencies or be explained by the influence of homologous data. None of the tested possible evolutionary and structural factors could explain the clusterization observed either. It looked as if certain protein sequence variations occurred and were fixed in the early course of evolution. Subsequent evolution (predominantly neutral) allowed only a limited number of changes and permitted new variants which led to preservation of certain k-tuples during the course of evolution. This was consistent with the theory of exon shuffling and protein block structure evolution. Possible applications of sequence space features found were also discussed.Correspondence to: H.A. Lim     

Molecular cloning of a chloroplastic proteinassociated with both the envelope and thylakoid membranes

Chloroplasts consist of six morphologically distinct compartments. Each compartment has a specific set of polypeptides that perform distinct biochemical functions. We report here the identification of a membrane-associated protein with a novel localization. This protein was synthesized as a 37 kDa precursor and was processed to a mature protein of 30 kDa after being imported into isolated pea chloroplasts. Fractionation of chloroplasts showed that the 30 kDa mature protein was associated with both of the envelope membranes as well as with thylakoid membranes. Immunocyto-chemical localization of the 30 kDa protein revealed that the protein occurred in clusters in the vicinity of both the envelope and the thylakoid. Possible functions of this 30 kDa protein, inferred from its novel localization pattern, are discussed.Abbreviations CAB light-harvesting chlorophyll a/b-binding protein of photosystem II - prCAB precursor protein to CAB - SS small subunit of ribulose-1,5-bisphosphate carboxylase - prSS precursor protein to SS - RCF relative centrifugation force     

Gravitropically-stimulated seedlings show autotropism in weightlessness

In a spaceflight experiment, autotropism by oat ( Avena sativa L.) coleoptiles following gravitropic responses was prominent in weightlessness: counter-reactions led to the straightening of the curved coleoptiles. This was not the case during clinorotation on earth. The autotropic reactions appeared to be related to the stimulus received during the stimulus period, i.e. the greater the response the greater the autotropic counter-reaction. Previous models of the gravitropic system which predicted that coleoptiles would not straighten in weightlessness are disproved. A modification to one of the models is proposed which includes the autotropic response observed in spaceflight. The nature of the counter-reactions in the absence of gravitropic stimulation is discussed.     

Distribution of unesterified and esterified pectins in cell walls of pollen tubes of flowering plants

Immunocytochemical localization of polygalacturonic acid (pectin) and methyl-esterified pectin in the walls of pollen tubes of 20 species of flowering plants grown in vitro was investigated by using monoclonal antibodies (MAbs) JIM5 and JIM7 and by means of confocal laser scanning microscopy (CLSM). In general, periodic annular deposits of pectins were found coating the tube wall in species possessing solid styles, and a more uniform pectin sheath in tube walls in species having hollow styles or no styles. We hypothesize that the periodic ring-like structure of the pectin sheath reinforces pollen tubes for passing through the transmitting tract in the style. Esterified pectin which prevents Ca²⁺-induced gelification of pectate is located predominantly at the apex. This implies that pectin esterification is related to tip wall loosening that is required for cell wall expansion during tip growth of pollen tubes. The occurrence of unesterified pectins in other areas of pollen tube walls suggests that de-esterification of pectin following tip expansion leads to a more rigid form of pectin that contributes to the construction of the pollen tube wall.     

The cortical actin cytoskeleton in a Dipteran embryo: Analysis of the spatial reorganization of F-actin aggregates during the early nuclear division cycles

Rhodamine phalloidin-staining was used to study the organization of the cortical actin cytoskeleton of the early Ceratitis capitata embryo. The dynamics of the actin aggregates and their changes in distribution during the formation of the syncytial blastoderm, were followed in detail. It was found that these aggregates formed a shell-like cluster around the interphase nuclei, and concentrated toward the poles of the mitotic apparatus when the nuclei divided. Laser scanning confocal microscopy revealed that aggregates not clustered at the poles of the mitotic apparatus were closely associated with fine fibers of a dense cytoplasmic network of actin filaments.     

犬传染性肝炎病毒在体外细胞质内的发生

通过对犬传染性肝炎病毒（ＩＣＨＶ）在犬肾传代细胞内形态发生及其抗原定位的电镜和免疫胶体金电镜研究,发现ＩＣＨＶ除了在宿主细胞核内发生外,还有一条细胞质内的发生途径。在细胞质内病毒核壳体的装配是以均质致密包涵体和副晶格包涵体为“基地”,这与人们熟知的细胞核内形态发生方式相似。免疫胶体金标记显示,细胞质包涵体中含有大量的ＩＣＨＶ抗原成分,显核壳体在细胞质内装配病毒的结构蛋白来源。此外,在感染的细胞质内还观察到与核内相同的病毒核心样结构。     

Cell Specificity of Molecular Changes During Memory Storage

Abstract: The aeolid nudibranch, Hermissenda crassicornis , exhibits Pavlovian conditioning to paired light and rotational stimuli and it has been suggested that protein kinase C (PKC) may play a critical role in the cellular mechanism for this conditioned behavioral response in the B-cell photoreceptor. The present study was designed to further examine learning-specific PKC involvement in identified cellular areas, particularly those in the visual-vestibular network, of the Hermissenda nervous system after Pavlovian conditioning. As used in previous vertebrate studies, the highly specific PKC radioligand, [³H]phorbol-12,13-dibutyrate ([³H]-PDBU), was used to determine the binding characteristics of the molluscan protein receptor considered to be PKC. The binding was specific, saturable, and could be displaced by a soluble diacylglycerol analogue. The binding activity was distributed evenly between the cytosol and the membrane. All of these analyses suggest that [³H]PDBU binds primarily to PKC in Hermissenda as it does in many other systems. Computerized grain image analysis was then used to determine the cellular localization of PKC as a function of Pavlovian conditioning. The medial and intermediate B photoreceptor and the optic ganglion showed significantly increased [³H]PDBU binding in conditioned animals. The present results provide the first report of an associative learning change of a key signal transduction component in identified neurons.     

Evolution of insect-plant relationships — a devil''s advocate approach

Most hypotheses concerning the evolution of insect-plant relationships are based on the assumptions that, (1) phytophagous insects reduce plant fitness, and that (2) insect-plant relationships are the result of unconstrained selection. It can be shown, however, that there is little evidence to support these assumptions. As an alternative, it is proposed that the evolution of insect-plant relationships results primarily from autonomous evolutionary events; namely from heritable functional changes within the insects' nervous system that determine plant recognition and ultimately host plant specificity. These changes cannot be evoked by selective ecological agents. They originate from intrinsic changes (mutationssensu lato) within the insect genome. Ecological factors play a secondary role: by either supporting or preventing the establishment of the new genotype with the novel food preference. This paper has been dedicated in warm friendship to Professor Louis M. Schoonhoven, the leading scientist in sensory physiology of phytophagous insects, on the occasion of his 60th birthday.     

Effect of dissolved inorganic carbon on the expression of carboxysomes,localization of Rubisco and the mode of inorganic carbon transport in cells of the cyanobacterium Synechococcus UTEX 625

In the cyanobacterium Synechococcus UTEX 625, the extent of expression of carboxysomes appeared dependent on the level of inorganic carbon (CO₂+HCO _inf3 ^sup- ) in the growth medium. In cells grown under 5% CO₂ and in those bubbled with air, carboxysomes were present in low numbers (<2 · longitudinal section^-1) and were distributed in an apparently random manner throughout the centroplasm. In contrast, cells grown in standing culture and those bubbled with 30 l CO₂ · 1^-1 possessed many carboxysomes (>8 · longitudinal section^-1). Moreover, carboxysomes in these cells were usually positioned near the cell periphery, aligned along the interface between the centroplasm and the photosynthetic thylakoids. This arrangement of carboxysomes coincided with the full induction of the HCO _inf3 ^sup- transport system that is involved in concentrating inorganic carbon within the cells for subsequent use in photosynthesis. Immunolocalization studies indicate that the Calvin cycle enzyme ribulose bisphosphate carboxylase was predominantly carboxysome-localized, regardless of the inorganic carbon concentration of the growth medium, while phosphoribulokinase was confined to the thylakoid region. It is postulated that the peripheral arrangement of carboxysomes may provide for more efficient photosynthetic utilization of the internal inorganic carbon pool in cells from cultures where carbon resources are limiting.Abbreviations Chl chlorophyll - DIC dissolved inorganic carbon (CO₂+HCO _inf3 ^sup- +CO _inf3 ^sup2- ) - PRK phosphoribulokinase - RuBP ribulose 1,5-bisphosphate - Rubisco LS large subunit of ribulose 1,5-bisphosphate carboxylase/oxygenase