Morphological taxonomy of little-differentiated Hyphomycetes

Morphological taxonomy of simple Hyphomycetes is complicated by the frequent occurrence of pleoanamorphism. In some groups of yeast-like fungi, uncommon synanamorphs are diagnostic. Differences in conidiogenesis do not always delimit natural groups. Some nomenclatural problems are mentioned, with an emphasis on the need of neotypification. Prospects are sketched for future taxonomic research.     

Starvation promotes Dictyostelium development by relieving PufA inhibition of PKA translation through the YakA kinase pathway.

When nutrients are depleted, Dictyostelium cells undergo cell cycle arrest and initiate a developmental program that ensures survival. The YakA protein kinase governs this transition by regulating the cell cycle, repressing growth-phase genes and inducing developmental genes. YakA mutants have a shortened cell cycle and do not initiate development. A suppressor of yakA that reverses most of the developmental defects of yakA- cells, but none of their growth defects was identified. The inactivated gene, pufA, encodes a member of the Puf protein family of translational regulators. Upon starvation, pufA- cells develop precociously and overexpress developmentally important proteins, including the catalytic subunit of cAMP-dependent protein kinase, PKA-C. Gel mobility-shift assays using a 200-base segment of PKA-C's mRNA as a probe reveals a complex with wild-type cell extracts, but not with pufA- cell extracts, suggesting the presence of a potential PufA recognition element in the PKA-C mRNA. PKA-C protein levels are low at the times of development when this complex is detectable, whereas when the complex is undetectable PKA-C levels are high. There is also an inverse relationship between PufA and PKA-C protein levels at all times of development in every mutant tested. Furthermore, expression of the putative PufA recognition elements in wild-type cells causes precocious aggregation and PKA-C overexpression, phenocopying a pufA mutation. Finally, YakA function is required for the decline of PufA protein and mRNA levels in the first 4 hours of development. We propose that PufA is a translational regulator that directly controls PKA-C synthesis and that YakA regulates the initiation of development by inhibiting the expression of PufA. Our work also suggests that Puf protein translational regulation evolved prior to the radiation of metazoan species.     

Poly(ADP-ribose) polymerase forms loops with DNA

The interaction between highly purified poly(ADP-ribose) polymerase from calf thymus and different topological forms of pBR322 DNA has been studied by gel retardation electrophoresis and electron microscopy. We show that: (i) in the absence of nicks on DNA the enzyme has a marked affinity for supercoiled (form I) DNA, (ii) in the presence of single stranded breaks poly(ADP-ribose) polymerase preferentially binds to form II, (iii) in all cases enzyme molecules are frequently located at DNA intersections, (iv) a cooperative binding of the enzyme on DNA occurs.     

Regulation of ATP synthesis catalyzed by the calcium pump of sarcoplasmic reticulum

The role of pH, KCl, ATP, water activity, and temperature in ATP synthesis from ADP and Pi was investigated in sarcoplasmic reticulum vesicles isolated from rabbit skeletal muscle. In totally aqueous medium, the synthesis of ATP was inhibited by ATP, KCl, and pH values above 6.5. When the water activity of the medium was decreased by the addition of 30% (v/v) dimethyl sulfoxide, the synthesis of ATP was no longer inhibited by ATP; it was activated by KCl and the optimum pH changed from 6.5 to 7.5. In totally aqueous medium, the concentration of MgCl2 needed for half-maximal synthesis of ATP was found to vary with the temperature of the assay medium; at 35 degrees C it was 1 mM and increased to a value higher than 10 mM when the temperature was decreased to 15 degrees C. In the presence of 30% dimethyl sulfoxide, maximal synthesis of ATP was attained in presence of 0.05 mM MgCl2 at both 15 and 35 degrees C. The hypothesis is raised that in the living cell water structure may play a role in regulating the synthesis of ATP observed during the reversal of the Ca2+ pump of the sarcoplasmic reticulum.     

Biology, serology and biochemistry of leucemogenic viruses derived from a radiation-induced tumor of C57BL mice

Two distinct rat propagates of a radiation leukemia virus (RadLV-Rs) from the C57BL mouse respectively induced characteristic leukemogenic effects. These were found to be related with the infection titers of the isolates, but not with either their antigenic specificities or their viral and proviral genome sequences.     

Microspectrophotometric and scanning microphotometric studies of carp (Cyprinus carpio L.) erythrocytes

Carp (Cyprinus carpio) hemoglobin readily autoxidizes in blood smears. Quantification of Soret-band absorbance in individual erythrocytes by means of scanning cytophotometry therefore requires more elaborate methods of preparation of blood samples. Of the fixatives that have been tested, suspension of whole blood in isotonic salt solutions containing glutaraldehyde was most suitable. Glutaraldehyde-fixed red blood cells are totally resistant to hemolysis. In the course of fixation, hemoglobin is transformed to methemoglobin. Spectrophotometry indicated extensive similarities between glutaraldehyde-fixed carp methemoglobin and human methemoglobin. In aqueous solutions, the intensity of the Soret-peak was pH-dependent. The allosteric modifier organic polyphosphate caused an R----T transition, resulting in increased molar extinctions. Dried preparations showed Soret-spectra that were not influenced from either pH or organic polyphosphate concentration of the aqueous suspensions in which the erythrocytes had been stored. The same was true for slide preparations of cyanomethemoglobin, easily derived from methemoglobin on addition of potassium cyanide. In the absence of oxygen fresh blood cells from carp slowly transform their hemoglobin into deoxyhemoglobin. Spectra of the intermediate stages of deoxygenation, Hb4(O2)3, Hb4(O2)2 and Hb4(O2), as well as mixtures of these intermediates, could be monitored.