Regulation of Gene Expression in Developing Zea mays Embryos: Protein Synthesis during Embryogenesis and Early Germination of Maize

Polypeptides synthesized in dissected embryos of Zea mays at different stages of embryogenesis and early germination have been characterized by their migration in two-dimensional gel electrophoresis. This analysis has been carried out with in vivo labeled polypeptides from excised embryos and with proteins synthesized in vitro in the rabbit reticulocyte system directed by poly(A⁺) RNA isolated from the different developmental stages. We have identified three main sets of expressed polypeptides: (a) embryonic set: this group of polypeptides is synthesized in young and mature embryos but not in early germination; (b) maturation set: this group of polypeptides is not present in young embryos and appears during the maturation period. Some of these polypeptides are still present in early germination while others disappear from stored mRNAs in dry embryos. One particular group from this set can be induced prematurely in young embryos by incubation with abscisic acid; and (c) germination set: this group of polypeptides is not expressed in the maturation period and appears after brief imbibition of the dry embryos.     

Essentiality of Boron for Dinitrogen Fixation in Anabaena sp. PCC 7119

The relationship between the requirement for boron and the form of N supplied in nutrient media to cyanobacterium Anabaena sp. PCC 7119 was investigated. When cells were grown in a medium which contained nitrate or ammonium-N, boron deficiency in the nutrient media did not inhibit growth or change cell composition. However, when cells were dependent on N₂ fixation, the lack of boron inhibited growth (i.e. growth ceased after 96 hours under these conditions). Additionally, boron-deficient cells showed a significant decrease in their content of phycobiliproteins and chlorophyll and accumulated carbohydrates within 24 hours of removing boron from the nutrient media. Inhibition of photosynthetic O₂ evolution accompanied the decrease in photosynthetic pigments. Boron deficiency symptoms were relieved when either boron or combined N was added to boron-deficient cultures. The degree of recovery depended upon the age of the cultures. Assays of nitrogenase activity showed that, after 2 hours of growth, nitrogenase activity of boron-deficient cells was inhibited by 40%. After 24 hours a total inactivation of nitrogenase activity was observed in boron-deficient cells. These results strongly suggest an involvement of boron in N₂ fixation in cyanobacteria.     

Bacteriophage-resistant mutants of Bacillus thuringiensis with decreased virulence in pupae of Hyalophora cecropia

Starting from a crystal-negative parental strain of Bacillus thuringiensis, we isolated certain bacteriophage-resistant mutants which showed decreased virulence in pupae of the cecropia moth (Hyalophora cecropia). These strains (class I mutants) were highly pleiotropic and showed resistance to seven or eight different phages, sensitivity to methicillin, and loss of flagella. They were also more sensitive to cecropia immune hemolymph in vitro. In addition, the export of at least three proteins was reduced. Revertants (class II mutants) were sensitive to phages, virulent, and resistant to penicillin derivatives. One class II mutant was a complete revertant in all properties examined. The other class II mutant was an incomplete revertant still susceptible to immune hemolymph and with repressed export of proteins. Virulence was not coupled to phage resistance as such or to lack of flagella because other mutants affected in these properties were virulent. Other factors which could be excluded as causes of virulence were production of extracellular protease and hemolysin.     

Two novel matrix proteins isolated from articular cartilage show wide distributions among connective tissues

Two proteins of Mr = 58,000 and 59,000, respectively, were purified from 4 M guanidinium chloride extracts of articular cartilage by dissociative CsCl-density gradient centrifugation followed by gel chromatography on Sephadex G-200 and ion exchange chromatography on DEAE-cellulose. The two proteins differ in ionic properties and only the one with Mr = 59,000 bound to the ion exchanger. Although the two proteins showed dissimilar peptide patterns after proteolysis, their amino acid composition was similar, with very high contents of leucine and aspartic acid/asparagine. The two proteins showed no cross-reactivity in radioimmunoassays. By use of these assays, the proteins were demonstrated in extracts of most connective tissues, with high contents of about 0.1% of tissue wet weight determined in several types of cartilage. Among the non-cartilage connective tissues, tendon and sclera had the highest contents of the proteins, i.e. about 0.1% of the tissue wet weight. Bone extracts, on the other hand, contained insignificant amounts of the proteins. Only the Mr = 59,000 protein was detected in serum, its concentration being about 33 micrograms/l. Both proteins were shown to be localized in the extracellular matrix of cartilage, predominantly in the territorial matrix, by using indirect immunofluorescence.     

Equilibrium binding of insulin to rat white fat cells at 15 degrees C

Equilibrium binding of insulin to isolated rat epididymal fat cells was investigated. A temperature of 15 degrees C was chosen for the study to minimize lysosomal degradation of insulin. Indeed, medium insulin lost only 1% of its precipitability in trichloroacetic acid during the 4-h incubation required to approach equilibrium. Binding was measured by a method that did not perturb the equilibrium of the system. A new formalism for analyzing binding data in general was introduced. A correction for trapping of insulin in the interstitial space of cell pellets was both necessary and sufficient to derive specific binding data from raw observations. Thus, so-called "nonspecific binding" was unmasked as a misnomer, and the expression "correction for trapping" was proposed as a substitute. Equations for one and two independent classes of binding sites were fit to the data by the method of maximum likelihood, and the best fit was selected based on Akaike's information criterion, as adapted for a constant fractional error. More than 99.7% of the binding sites were found to be describable by a simple binding isotherm with Kd,app = 8.8 multiplied by over divided by 1.3 nM. Less than 0.3% sites had a higher affinity (Kd approximately equal to 8 multiplied by over divided by 3 pM). There were 99,000 x/divided by 1.6 binding sites/cell. These equilibrium parameters are in agreement with values derived from a kinetic analysis, presented in the subsequent paper (Lipkin, E. W., Teller, D. C., and de Ha?n, C. (1986) J. Biol. Chem. 260, 1702-1711).     

Molecular characterization of the in situ red cell membrane calcium pump by limited proteolysis

In inside-out red cell membrane vesicles active calcium transport and the formation of the enzyme-phosphate complex (EP) of the calcium pump were simultaneously investigated and the effects of a limited proteolytic digestion examined. In order to visualize the proteolyzed EP forms we have induced the formation of a maximum level EP from [gamma-32P]ATP in the presence of Ca2+ + La3+ and applied a good-resolution acidic discontinuous sodium dodecyl sulfate-polyacrylamide gel electrophoresis system. Proteolysis of inside-out vesicle membranes by trypsin, Pronase, papain, or chymotrypsin produces a calmodulin-like activation of the calcium pump, abolishes its calmodulin sensitivity, and decreases the original 140-kDa EP complex to a limit polypeptide of 80 kDa. Trypsin digestion produces another major intermediary fragment of 90 kDa, which is still a low-activity calmodulin-sensitive form of the pump. The red cell calcium pump is activated by trypsin both in the absence and presence of Ca2+ during digestion although the rate of activation and the appearance of the 80-kDa polypeptide are enhanced by Ca2+. If proteolytic digestion is carried out by chymotrypsin, a calmodulin-insensitive maximum activation of the calcium pump coincides with the formation of a 125-130-kDa EP-forming polypeptide. Chymotrypsin and carboxypeptidase A have synergistic effects on the formation of this latter high-activity species. Based on these data we suggest a probable molecular arrangement for the functional parts of the red cell membrane calcium pump.     

Contribution to the ecology ofMarsilea quadrifolia L.

Data are presented on the aboveground and underground biomass of the speciesMarsilea quadrifolia and on the water regime and soil conditions in a habitat of this species in Central Europe (Czechoslovakia).     

Computer-assisted mathematical analysis of sigmoid biological events

A program in BASIC is described which allows accurate quantificationof some numerical parameters that can be objectively correlatedto biological indexes in sigmoid biological events. Attentionwas focused on the polymerization process of actin (a muscleprotein with a mol. wt of 42 000 daltons) studied as the variationin the OD₃₆₀ index with time. The experimental points, if plotted,can be well approximated by a rational function of the typeOD₃₆₀ = f(t), which passes through the origin and can be representedgraphically by a sigmoid curve. The program was very helpfulin comparing the experimental curves and in analysing significantparameters, such as maximum velocity and asymptote, that characterizethese curves and whose interpretation would otherwise be purelysubjective. Received on July 11, 1985; accepted on January 13, 1986