Dynamic view of the nuclear matrix.

The nuclear matrix is an operationally defined nuclear skeletal structure that is believed to be involved in many nuclear functions including DNA replication, transcription, repair, and prem RNA processing/transport. Until relatively recently, the nuclear matrix was thought to be a rigid and static structure, but it is now thought to be dynamic. This paradigm shift was based in part on the tracking of the intranuclear movement of proteins tagged with fluorochromes. In this review, we attempt to redefine the nuclear matrix in light of recent findings and describe some useful techniques for the dynamic analysis of nuclear function.</p

The presence of phosphate-binding protein in inner mitochondrial membrane

Phosphate-binding protein(s) was found in the inner mitochondrial membrane of calf heart by Sephadex G-200 and G-25 gel filtration. The binding activity was inhibited by N-ethylmaleimide and competed by a large amount of cold phosphate. The amount of phosphate bound to the fraction was 29 nmoles per mg of protein. Affinity chromatography with phosphate-bound Sepharose 4B confirmed the presence of phosphate-binding protein(s) in the active fraction of mitochondrial membrane fractionated by gel filtration.</p

Role of hydrophobic interaction in hapten-antibody binding

The precipitation reaction of bovine serum albumin coupled with p-azophenylleucine with homologous antibody was inhibited by several structurally related haptens. The isobutyl group substituent on alpha-carbon atom of the leucine residue contributed more than -5.8 Kcal/mol to the free energy of binding. This value was consistent with the free energy change expected from the transfer of n-butane from an aqueous environment to liquid n-butane. The observed contribution was explained, in terms of the hydrophobic interaction of the isobutyl group with the antigen binding site of the antibody molecule. These results were also compared with other hapten-antibody systems.</p

A dynamic code for economic object valuation in prefrontal cortex neurons.

Neuronal reward valuations provide the physiological basis for economic behaviour. Yet, how such valuations are converted to economic decisions remains unclear. Here we show that the dorsolateral prefrontal cortex (DLPFC) implements a flexible value code based on object-specific valuations by single neurons. As monkeys perform a reward-based foraging task, individual DLPFC neurons signal the value of specific choice objects derived from recent experience. These neuronal object values satisfy principles of competitive choice mechanisms, track performance fluctuations and follow predictions of a classical behavioural model (Herrnstein's matching law). Individual neurons dynamically encode both, the updating of object values from recently experienced rewards, and their subsequent conversion to object choices during decision-making. Decoding from unselected populations enables a read-out of motivational and decision variables not emphasized by individual neurons. These findings suggest a dynamic single-neuron and population value code in DLPFC that advances from reward experiences to economic object values and future choices.Wellcome Trust, Behavioural and Clinical Neuroscience Institute (BCNI) Cambridg

Difference in the homology of two nuclear nonhistone protein fractions as compared by polyacrylamide gel electrophoresis.

The extent of homology between two protein fractions was compared by simple electrophoretic analysis. Nuclear proteins of several rodent cells of different origins were fractionated into acid-soluble and acid-insoluble fractions. The two protein fractions were subjected to polyacrylamide gel electrophoresis in separate gel systems, and protein bands with identical mobilities were sought either in all possible combinational pairs of cell types or in all cell types. The paired and overall homology indices calculated from these data and chi-square testing of the results indicated that acid-soluble nuclear nonhistone proteins are more homologous than acid-insoluble nuclear proteins. Several factors which might have affected the results were discussed.</p

Unique features of monoclonal IgG2b in the cleavage reaction with pepsin.

Preparations of IgG2b purified from several mouse hybridoma clones were highly susceptible, compared to other subclasses, to peptic digestion under conditions usually used to prepare F (ab')2 fragments. Analyses of the digestion products revealed that no F (ab')2 was produced and that the main product was a Fab-like fragment. Demonstration of the hinge disulfides in the Fc portion clearly indicated that in IgG2b the primary peptic cleavage occurs on the NH2-terminal side of the inter-heavy chain disulfide bridge. The resulting Fab failed to bind with antigen, suggesting the importance of the CH1-hinge region in maintaining the native conformation of the antigen-binding site.</p

Partial purification and properties of bovine heart catalase.

Catalase was partially purified (about 380-fold purification) from the post-mitochondrial supernatant of bovine heart and compared with catalases from bovine erythrocytes and bovine liver. The electrophoretic mobility in polyacrylamide gel (pH 8.0) of heart catalase was the same as that of erythrocyte catalase and was smaller than that of the liver enzyme. The heart catalase was indistinguishable from erythrocyte catalase in regard to the molecular weights of subunit polypeptides, the inhibition patterns produced by several catalase inhibitors, and specific activity. The pH-activity curve of heart catalase consisted of a characteristic biphasic pattern with a peak at pH 7.5 and a shoulder at pH 10.</p

Susceptibility of Rous sarcoma virus-specific sequences integrated into SR-C3H/He mouse ascites sarcoma cell chromatin to DNase I and DNase II.

The susceptibility of Rous sarcoma virus (RSV) genomes integrated in mouse ascites sarcoma cells (SR-C3H/He cells) to DNase I and DNase II was investigated. Approximately half of the viral sequences were sensitive to DNase I and DNase II when 17% and 7.4% of the chromatin DNA was rendered acid soluble, respectively. The results suggest that newly acquired exogenous proviral sequences are integrated into both transcriptionally active and inactive regions of chromatin in cells lacking related endogenous viral sequences.</p