Turnix maculosa obiensis subsp. nova

Ohne Zusammenfassung     

Transformation of Penicillium chrysogenum by a vector containing a mitochondrial origin of replication

Summary In order to establish a transformation system for P. chrysogenum autonomously replicating vectors were constructed using mitochondrial DNA sequences from the fungus. A physical map of the mt DNA of a production strain was established using ten different restriction enzymes. Unexpectedly, the mt DNA of this strain proved to be significantly smaller than that of a second strain from a culture collection (27 kb versus 49 kb). Various fragments representing about 71% of the 27 kb mt DNA were cloned and, at first, preselected for replicating activity in an intermediate host (Saccharomyces cerevisiae). Two of these fragments also promoted autonomous replication in P. chrysogenum, which was confirmed by isolation of bulk DNA and transfer into E. coli. For selection of transformants in P. chrysogenum the prokaryotic kanamycin resistance gene was used which increased about twofold the resistance against G418. Present address: Institut für Biotechnologie, Fachgebiet Mikrobiologie, Techn. Universität Berlin, Seestr. 13, D-1000 Berlin 65     

Carbohydrate formation in rewetted terrestrial cyanobacteria

Summary In the terrestrial cyanobacterium Nostoc commune Vauch. formation of carbohydrate polymers was measured upon rewetting the mats in a light-dark regime. To discriminate between carbohydrates of different physiological function, total carbohydrate was determined as anthrone-reactive material (ARM) and storage carbohydrate (glycogen) assayed by an enzymic test. In the dry thalli glycogen was found to represent less than one tenth of the ARM. After rewetting an increase of total carbohydrate was observed in illuminated samples. Only glycogen, however, showed a regular pattern of synthesis and degradation during a 12:12 h light-dark cycle. This indicates that most carbohydrates detected by anthrone belong to the metabolically inert sheath material.When illuminated colonies were kept submerged after rewetting glycogen was hydrolyzed indicative of being used in the rapid recovery of cellular functions as observed in rewetted colonies. Apparently, photosynthesis allowed for net glycogen synthesis only, provided the mats were sufficiently aerated. These findings give evidence that the (carbohydrate) sheath plays an important role in water retention in an organism bound to a terrestrial habitat.     

The three-dimensional structure of ricin at 2.8 A

The x-ray crystallographic structure of the heterodimeric plant toxin ricin has been determined at 2.8-A resolution. The A chain enzyme is a globular protein with extensive secondary structure and a reasonably prominent cleft assumed to be the active site. The B chain lectin folds into two topologically similar domains, each binding lactose in a shallow cleft. In each site a glutamine residue forms a hydrogen bond to the OH-4 of galactose, accounting for the epimerimic specificity of binding. The interface between the A and B chains shows some hydrophobic contacts in which proline and phenylalanine side chains play a prominent role.     

Functional and structural characterization of the two beta 1-adrenoceptor forms in turkey erythrocytes with molecular masses of 50 and 40 kilodaltons

We have previously described a specific protease in turkey erythrocytes that converts the larger 50-kDa (P50) form of the beta 1-adrenoceptor to a smaller 40-kDa (P40) form [Jürss, R., Hekman, M., & Helmreich, E. J. M. (1985) Biochemistry 24, 3349-3354]. Further functional and structural characterization studies of the two forms are reported here. When purified P50 and P40 receptors were compared with respect to their relative capabilities to couple in lipid vesicles with pure stimulatory G-proteins (Gs-proteins) prepared from turkey erythrocytes or rabbit liver, a faster and larger activation of Gs-proteins was observed in response to l-isoproterenol and guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) with P40 than with P50 receptor. The kon values for P40 were 0.47 min-1 in the case of liver Gs and 0.22 min-1 in the case of erythrocyte Gs, whereas the corresponding values for P50 were 0.34 min-1 and 0.12 min-1, respectively. The binding properties of P50 and P40 forms of the receptor were not different, and desensitization of turkey erythrocytes on exposure to l-isoproterenol did not activate the protease. We furthermore ascertained that only the larger form with a molecular mass of 50 kDa carries the N-linked carbohydrates, which are removed on proteolytic conversion to the 40-kDa form and have either a triantennary or a tetraantennary nonfucosylated complex-type structure containing terminal sialyl residues.     

Temperature jump study of charge translocation during the bacteriorhodopsin photocycle

Temperature jump experiments were carried out on purple membranes oriented and fixed in polyacrylamide gel. With green background illumination a relaxation of the photocurrent after an infrared laser pulse could be observed. To simulate the temperature jump signals different models of the bacteriorhodopsin photocycle were tested. The parameters of these models were obtained by measuring absorbance changes and photocurrent after excitation with a 575-nm laser flash.

A model with a temperature-dependent branching before the M state turned out to be satisfying. Other models, especially those with a late branching or without branching, could not reproduce the temperature jump measurements.

     

Sea urchin oocytes possess elaborate cortical arrays of microfilaments, microtubules, and intermediate filaments

Extensive arrays of microfilaments, microtubules and cytokeratin-type intermediate filaments were detected in the cortex of Strongylocentrotus droebachiensis oocytes using fluorescently labeled antibodies on both cortex and whole mount preparations. All three filament systems undergo dramatic structural reorganization during meiotic maturation of the egg. Microfilaments form a dense meshwork within the cortex of the oocyte. After meiosis, the filaments rearrange and shorten, resulting in a more loosely organized network. Both cortical microtubules and microtubules associated with a microtubule-organizing center are observed within the oocyte. After meiosis, the number and length of the cortical microtubules gradually diminish. A microtubule organizing center is found situated between the germinal vesicle and the plasma membrane in many oocytes. A network of filaments extends from the microtubule organizing center and radiates peripherally toward the germinal vesicle, presumably marking the animal pole. Cytokeratin-like intermediate filaments form a reticular network within the oocyte cortex, then solubilize during meiosis. In whole mounts of oocytes there is a single focal center of cytokeratin staining from which filaments radiate. Indirect immunofluorescence experiments, using anti-tubulin and anti-cytokeratin antibodies simultaneously, reveal the intermediate filament focal center to be localized within the microtubule organizing center. These results demonstrate the presence of a complex cortical cytoskeleton in premeiotic eggs of the sea urchin, Strongylocentrotus droebachiensis.