THE HUMAN CHROMOSOME : Electron Microscopic Observations on Chromatin Fiber Organization

Human lymphocytes were grown in short-term tissue culture and were arrested in metaphase with Colcemid. Their chromosomes were prepared by the Langmuir trough-critical point drying technique and were examined under the electron microscope. In addition, some chromosomes were digested with trypsin, Pronase, or DNase. The chromosomes consist entirely of tightly packed, 240 ± 50-A chromatin fibers. Trypsin and Pronase treatments induce relaxation of fiber packing and reveal certain underlying fiber arrangements. Furthermore, trypsin treatment demonstrates that the chromatin fiber has a 25–50 A trypsin-resistant core surrounded by a trypsin-sensitive sheath. DNase digestion suggests that this core contains DNA.     

FINE STRUCTURE OF PACINIAN CORPUSCLES IN THE MESENTERY OF THE CAT

Pacinian corpuscles in the mesentery of adult cats were fixed with either glutaraldehyde, osmium tetroxide or permanganate solutions by close intra-arterial injection through the mesenteric artery, and were processed, after electron staining and Epon embedding, for electron microscopy. Better resolution of the corpuscle's ultrastructure was obtained than available heretofore. The myelinated segment of the corpuscle contains blood vessels separated from the axon by collagen fibers and 3 to 4 layers of lamellae. No blood vessels are found in the central core, though access from the vessels is afforded by diffusion through the "cleft" of the inner core. Two cell types are discernible in the inner core hemilamellae; the "clear cells" in which pinocytotic vesicles and organelles abound and reflect the greater metabolic activity of these cells, in contrast to the "dark cells." The ultraterminal is ellipsoidal in form with projections into the "cleft" which give this portion an irregular appearance in section. The terminal and ultraterminal are packed with mitochondria, and "synaptic" vesicles are seen in the ultraterminal. The innermost laminae of the inner core cells are in close apposition to the terminal and break their regular pattern of hemilamellation to surround the small ultraterminal projections at the apical part of the corpuscle.     

Electron Microscopic Observations on the Ribonucleic Acid of Murine Leukemia Virus

The ribonucleic acid (RNA) of murine leukemia virus (MLV) Rauscher strain was observed by the aid of electron microscopy with the use of the protein monolayer technique. RNA was observed directly after release from virus particles or after isolation by sedimentation in sucrose density gradients. Molecules were found in an extended linear form. Many of the RNA filaments released by detergent treatment contained curled regions, suggesting the linear filaments were originally coiled within the virus particle. The relationship of the curled areas to the containment of the RNA within the virus particle is discussed, and a mechanism for the inclusion of RNA in the budding virion is proposed. Treatment of the extended MLV-RNA with dimethyl sulfoxide resulted in the collapse of the molecule forming a tangled complex. Treatment with urea or heating at 50 C in 3 mm NaCl also produced this effect. Also under the conditions in which MLV-RNA was linear, RNA from Rous sarcoma virus also was linear, but Newcastle disease virus RNA and ribosomal RNA of rat liver had collapsed structures. The results indicated that the RNA of MLV, and perhaps other RNA-containing tumor viruses, has a specific unique conformation dependent upon hydrogen bonds.     

Nature of Escherichia coli B(P1) Yielder Cells at the Time of Infection with Restricted T1

In the infection of Escherichia coli B(P1) with restricted T1, it was shown that yielder cells consist of both special and nonspecial cells. Special or predetermined yielders occurred only among the earliest yielders. In most instances, yielder-cell formation was most easily explained by assuming that the first step was a chance escape of the restricted phage DNA from the degrading enzyme of the restricting cell.     

Genetic studies of the ribosomal proteins in Escherichia. coli. II. Altered 30s ribosomal protein component specific to spectinomycin resistant mutants

Summary Spectinomycin resistant (spc ^r) mutants were obtained by treating the cells of E. coli K12, W3637 with nitrosoguanidine. The compositions of ribosomal proteins were analyzed for six out of eleven such spc ^r-mutants with chromatography on a carboxymethyl cellulose (CMC) column. The 30s ribosomal subunit from all of the spc ^r-mutants was found to contain the altered 30-4 protein component, while no difference was detected in 50s ribosomal proteins between spc ^r and spc ^s bacteria.Abbreviations used CMC carboxymethyl cellulose - str streptomycin - spc spectinomycin     

Influence of the Maize Dwarf Mosaic Virns and Simazine upon the Buffer Soluble Proteins and Catalase Activity of a Virus-susceptible and a Virus-tolerant Variety of Zea mays

Inbred corn varieties differing in their tolerance to the maize dwarf mosaic virus infection also differ in varietal character and host response to simazine. Oh 7B, a tolerant cv., has less total soluble and globulin proteins than the sensitive variety, H 55, but more Kjeldahl nitrogen, albumin protein and a doubling of catalase activity. Virus inoculation in Oh 7B causes a reduction in all three protein fractions, Kjeldahl nitrogen and catalase activity. Deleterious virus-simazine interaction does not occur with either variety and the observed varietal and host response differences in protein may account for the conflicting reports of other workers.     

The thermal polymerization of orosomucoid

1. Orosomucoid was prepared from the urine of a nephrotic patient and polymerized by heating it in a range of salt concentrations at pH4·1. 2. Heating at low ionic strengths produced a `chain' polymer of indefinite length but having the same width as the diameter of the monomer (5·0nm.). Similar treatment in high ionic strengths also produced a spherical (`ball') polymer of limited diameter (14·8nm.). 3. The size and shape of both polymers were determined from ultra-centrifuge, gel-filtration and electron-microscope results. The results suggest that eight monomer units condense to form the ball polymer. 4. Heating orosomucoid at pH1·8 hydrolysed the N-acetylneuraminic acid off the molecule; only chains could then be formed, even in high ionic strengths. 5. Both polymers were stable under normal conditions but could be depolymerized in 3m-guanidine hydrochloride. The monomer could be repolymerized on heating: the `chain monomer' only formed chains at all ionic strengths, but the `ball monomer' was indistinguishable from the original monomer in its immunological properties and polymerization reaction.     

Schiff bases formed from retinal and phosphatidylethanolamine, phosphatidylserine, ethanolamine or serine

1. Conditions were established for the reaction of retinal with phosphatidylethanolamine, phosphatidylserine, ethanolamine and serine in chloroform, ethanol or ethanol–water solutions to form retinylidene compounds, or Schiff bases. 2. The Schiff bases were reduced to retinyl compounds with sodium borohydride. 3. Absorption maxima and molar extinction coefficients were determined for the various retinylidene and retinyl compounds and for the corresponding coloured products formed by their reaction with antimony trichloride.