Studies of the interaction of RecA protein with DNA

Ethidium fluorescence assays were adapted for the rapid and sensitive detection of precA; in addition, fluorescence measurements on binding precA to linear, OC and CCC PM2 DNAs have enabled the stoichiometry of precA binding as well as the precA-induced unwinding angle of DNA to be determined. The stoichiometry of binding was independently confirmed by sedimentation analysis to be one precA molecule per 3 bp. The unwinding angle was also independently confirmed by measurements of fluorescence changes induced by the binding of precA to CCC DNA which was relaxed by topoisomerase to give a precA-induced unwinding angle of 51 degrees. Electron microscopy of OC DNA molecules which bound nonsaturating amounts of precA revealed that the length increase in DNA due to precA was approximately 55%. Finally, examination of negatively stained precA complexes with a variety of linear DNAs showed that the minor groove is the primary site of interaction for this protein.     

Chemical Nature of Malty Flavor and Aroma Produced by Streptococcus lactis var. maltigenes

Mature skim milk cultures of Streptococcus lactis var. maltigenes were steam distilled at low temperature under reduced pressure. Ethyl ether extracts were prepared from the distillates and analyzed by gas-liquid chromatography and mass spectrometry. Twenty of 31 components detected in the culture distillates were identified positively and 11 tentatively, whereas 10 of 19 components detected in the heated skim milk control were identified positively and 9 tentatively. Among components detected in the culture distillate, but not detected in the heated skim milk distillate, and which have not been previously identified in milk cultures of the organism were phenylacetaldehyde and phenethanol. Quantitative analyses of the volatiles entrained from milk cultures of several strains of S. lactis var. maltigenes revealed a probable relationship between variation in the character of the aroma of the cultures and the alcohol/aldehyde ratio.     

Isolation of brain tubulin by affinity chromatography

An affinity chromatographic procedure for the isolation of tubulin from brain is described. The yield is good and the method rapid and gentle. Criteria of purity are colchicine binding, SDS acrylamide gel electrophoresis, and velocity sedimentation.     

Structure and Development of Viruses as Observed in the Electron Microscope: X. Entry and Uncoating of Adenovirus

Stages in the direct penetration of adenovirus through the cell membrane are illustrated. Phagocytosis with rupture of the vacuole and release of virus into the cytoplasm may also account for entry of some particles. Uncoating by digestion within phagosomes was not observed. Rather, alteration of capsid and core occurred to virions free in the cytoplasm. Nucleoprotein released from virus close to the nucleus was transported to the nuclear matrix by a unique mechanism. These events were not prevented by puromycin and hence were not dependent upon the synthesis of new enzymes. They were, however, energy-dependent.     

Stimulation of ethylene evolution and abscission in cotton by 2-chloroethanephosphonic Acid

Ethrel, a mixture of 2-chloroethanephosphonic acid and its ethyl ester, hastens abscission of leaves, debladed petioles, and flower buds of cotton plants (Gossypium hirsutum, L.). Both young and old leaves abscissed while still green. Application of Ethrel stimulated evolution of ethylene, and this response preceded abscission. Air concentrations of ethylene around enclosed, treated-plants were adequate to produce abscission in plants. Non-treated plants defoliated when enclosed with plants sprayed with Ethrel. The stimulation of abscission of explant petioles by Ethrel was reversed by naphthalene acetic acid. The stimulation of abscission by Ethrel was concluded to be mediated by ethylene.     

Acetazolamide and Sodium Bicarbonate in Treatment of Salicylate Poisoning in Adults

Ten adults suffering from salicylate overdosage were treated successfully with a combination of sodium bicarbonate and acetazolamide to exploit the increase in salicylate clearance which is known to occur in very alkaline urine. The advantages of the method include the absence of important complications and the small volume of fluid required.     

Synaptosomal protein synthesis in a cell-free system

—Synaptosomes were isolated from cerebral cortex of young rats and incubated with ¹⁴C-labelled l -leucine in vitro. Amino acid incorporation into proteins of the synaptosomal cytoplasm, mitochondria and membrane components was observed. There was no incorporation into proteins of the vesicles. The protein-synthesizing system was not stimulated by the addition of either ATP or an ATP-generating system. ATP at all concentrations was inhibitory. Two different protein-synthesizing systems operate in the synaptosome. One, sensitive to inhibition by chloramphenicol and related antibiotics, is found in the mitochondrial subfraction and the other, inhibited by cycloheximide, is located either in the membrane components or the synaptosomal cytoplasm. This second system resembles the eukaryotic ribosomal system in its sensitivity to cycloheximide. Both the synaptosomal soluble fraction and the synaptosomal membrane fractions were shown previously to contain RNA. This RNA could function in protein-synthesizing mechanisms in the synaptosome. These results deomonstrate that protein is synthesized in axonal components and show that it is unnecessary to postulate that all axonal protein is supplied by somato-axonal flow.