Incompatibility in Podospora anserina: Comparative Properties of the Antagonistic Cytoplasmic Factors of a Nonallelic System

In the fungus Podospora anserina, the interaction between the nonallelic incompatible R and V genes has two consequences: a lytic reaction due to the synthesis of specific proteolytic enzymes, and a quenching in protein and ribonucleic acid synthesis. The incompatibility reaction when vegetative or sexual R and V cells fuse is asymmetric: it is induced only in the R protoplasm. The cessation in ribonucleic acid and protein synthesis was investigated in heterokaryotic strains carrying the antagonistic R and V genes and their "neutral" r and v alleles. Asymmetry between R and V genes lies in the fact that the strains homozygous for the R genes are the only strains that cannot grow. From these results it is postulated that the V-gene product is a diffusible cytoplasmic factor and that the R-gene product, which is nonautonomous, is a ribosomal component.     

Short- and Long-Term Alterations of Gene Expression in Limbic Structures by Repeated Electroconvulsive-Induced Seizures

Rats were submitted to a series of 10 daily electroconvulsive shocks (ECS). A first group of animals was killed 1 day after the last seizure and a second group 30 days later. Tyrosine hydroxylase (TH) activity was measured using an in vitro assay in the nucleus caudatus, anterior cortex, amygdala, substantia nigra, ventral tegmental area, and locus ceruleus. The mRNA corresponding to this enzyme (TH-mRNA) was evaluated using a cDNA probe at the cellular level in the ventral tegmental area, substantia nigra, and locus ceruleus. Met-enkephalin (MET)-immunoreactivity and the mRNA coding for the preproenkephalin (PPE-mRNA) were assayed in striatum and the central nucleus of the amygdala. The day after the last ECS an increase of TH activity was observed in the ventral tegmental area, locus ceruleus, and substantia nigra in parallel with a similar increase in the amygdala and striatum; in the anterior cortex TH activity remained unchanged. TH-mRNA was increased in the locus ceruleus, evidencing the presence in this structure of a genomic activation. The amounts of MET and PPE-mRNA were unaffected in the striatum but increased in the amygdala. Thirty days after the last ECS we observed a decrease of TH activity in the amygdala and of TH-mRNA amount in the ventral tegmental area. In the locus ceruleus TH-mRNA remained higher in treated animals than in controls whereas TH activity returned to control levels. These results demonstrate that a series of ECS induces an initial increase of the activity of mesoamygdaloid catecholaminergic neurons followed by a sustained decrease through alterations of TH gene expression which could mediate the clinical effect of the treatment.     

Comparison of different cationic probes for electron microscopic visualization of bacterial polyanionic capsular material

We have isolated from the ovine rumen eight bacterial strains belonging to the speciesButyrivibrio fibrisolvens. DNA hybridization studies showed that the eight strains could be divided into four homology groups, of which none was closely related to the type strain ATCC 19171. Measurement of cross-hybridization between selected pairs of bacterial strains showed that DNA types which produced low, but significant, cross-hybridization on dot-blots were able to form heteroduplexes with between 8.4% and 32.9% of the efficiency of homoduplex formation. Thermal denaturation of the same heteroduplexes resulted in Tm values 6.4–7.5°C lower than those of the homologous duplexes formed under the same conditions. In some cases, hybridization between strains was below the level of reliable measurement. Similar experiments with ten recently isolated strains ofBacteroides ruminicola sub-sp.brevis revealed a similar degree of genetic divergence between isolates.     

Epidermal growth factor receptor binding is not a simple one-step process

The binding kinetics of 125I-labeled mouse epidermal growth factor (EGF) to receptors on human fibroblast cells in monolayer culture were measured at 4 degrees C. Initial binding rates as a function of hormone concentration allowed estimation of simple two-state on-off rate constants of 1.2 x 10(6) M-1 s-1 and 4.9 x 10(-3) s-1, respectively. These two-state parameters gave inadequate computer fits to long term kinetic and equilibrium-binding data, suggesting that an additional process(es) was occurring. Nonlinear equilibrium Scatchard plots and transient "pseudo-Scatchard" plots taken at pre-equilibrium times support the idea that at least one other process is occurring during receptor binding. 125I-EGF-receptor dissociation kinetic plots were biphasic, yielding rate constants of 1.5 x 10(-2) s-1 and 5.6 x 10(-5) s-1 with the ratio of the two components changing with the time of initial incubation with 125I-EGF. Application of a ternary complex model which assumed complexation of the bound receptor with a cell surface interaction molecule gave satisfactory fits to all data.