The ultrastructural basis of the permeability of arterial endothelium to horseradish peroxidase

The thoracic aorta and basilar artery, in which the incidence of atherosclerosis is known to be different, were examined to elucidate the correlation between the structure of the intercellular cleft junction between adjacent endothelial cells and its permeability to HRP. Tannic acid or HRP in the vessel lumen passed through the intercellular clefts of the thoracic aorta into the subendothelial space, whereas in the basilar artery they were unable to penetrate beyond the tight junction of the intercellular clefts. Freeze-fracture replicas revealed that the tight junctions of the thoracic aorta consisted of one to two junctional strands in most areas of the cleaved planes, with discontinuities in some places, whereas those of the basilar artery consisted of a continuous belt-like meshwork of six anastomosing junctional strands on average. These observations confirm that the structure of endothelial junctions in arteries has a close correlation with the permeability of the intercellular clefts to HRP.     

Rapid isolation of nucleoli from detergent purified nuclei of various tumor and tissue culture cells

A rapid isolation procedure of nucleoli from detergent purified nuclei of some tumor and tissue culture cells is described. The procedure makes use of a non-ionic detergent, Nonidet P40 and sodium deoxycholate to purify nuclei followed by the addition of Ca²⁺ or Mg²⁺ to strengthen the nucleoli against sonication. Enzymatically active (with respect to nucleolar RNA polymerase) nucleoli containing undegraded nucleolar RNAs may be isolated from a mouse hepatoma MH134, Ehrlich ascites tumor, HeLa cells, L cells and C3H2K cells with this procedure.     

Phenethyl Alcohol Resistance in ESCHERICHIA COLI. III. a Temperature-Sensitive Mutation (dnaP) Affecting DNA Replication

A temperature-sensitive DNA replication mutant of E. coli K-12 was isolated among the mutants selected for phenethyl alcohol resistance at low temperatures. This mutation, designated as dnaP18, affects sensitivity of the cell to phenethyl alcohol, sodium deoxycholate and rifampicin, presumably due to an alteration in the membrane structure. At high temperatures (e.g., 42 degrees ), synthesis of DNA, but not RNA or protein, is arrested, leading to the formation of "filaments" in which no septum formation is apparent. Nucleoids observed under electron microscope seem to become dispersed and DNA fibrils less condensed, which may explain the loss of viability under these conditions. Genetic analyses, including reversion studies, indicate that a recessive dnaP mutation located between cya and metE on the chromosome is responsible for both alterations of the membrane properties and temperature sensitivity. The dnaP18 mutation does not affect growth of phage T4 or lambda under conditions where host DNA replication is completely inhibited. Kinetic studies of DNA replication and cell division in this mutant after the temperature shift from 30 to 42 degrees , and during the subsequent recovery at 30 degrees , accumulated evidence suggesting that DNA replication comes to a halt at 42 degrees upon completion of a cycle already initiated before the temperature shift. Since the recovery of DNA synthesis after exposure to 42 degrees does not depend on protein or RNA synthesis or other energy-requiring processes, the product of the mutant dnaP gene appears to be reversibly inactivated at 42 degrees . Taken together with the recessive nature of the present mutation, it was suggested that one of the membrane proteins involved in initiation of DNA replication is affected in this mutant.     

X-ray equatorial diffraction studies on the cross-sectional structure of Salmonella flagella

X-ray diffraction studies have been made on the cross-sectional structure of the normal Salmonella flagella. Two approaches have been made: one based upon small-angle equatorial scatterings (2θ 3°) and the other upon moderate-angle angle equatorial diffractions (3° 2θ 10°).Analysis of small-angle scattering data gives the radius of gyration of the flagella as 68 Å. Cylindrically averaged electron density of the cross-section of the flagella is obtained by means of the Fourier-Bessel transformation method. The average radius of the flagella is about 65 Å.In the investigation of the moderate-angle diffraction pattern, validity is examined of the model that a flagellum consits annularly arranged strands, of which each has a cylindrically symmetric structure. Features of the pattern observed in the range of 3° < 2θ < 10° can be interpreted fairly well by this model. Average radii of the flagella obtained for the 11 and 13 strands models are close to that obtained by the analysis of the small-angle scattering data.     

Clinical Use of a New Mitral Disc Valve

A disc valve of new design was used successfully for the replacement of the mitral valve in patients with rheumatic mitral valve disease. This valve would appear to have the following advantages over the mitral ball valve prosthesis:• Lower left atrial pressure after replacement.• Elimination of the hazard of left ventricular outflow tract obstruction with mitral valve replacement.• Decreased incidence of thromboembolization.• Abolition of possibility of ventricular septal irritation.Despite the better outlook for this valve compared with the ball valve for mitral valve substitution, the mitral valve should always be repaired whenever feasible. Repair is possible in the majority of patients.