Reductive alkylation of ribosomes as a probe to the topography of ribosomal proteins

Escherichia coli ribosomes were treated with a number of different aldehydes of various sizes in the presence of NaBH(4). After incorporation of either (3)H or (14)C, the ribosomal proteins were separated by two-dimensional polyacrylamide-gel electrophoresis and the extent of alkylation of the lysine residues in each protein was measured. The same pattern of alkylation was observed with the four reagents used, namely formaldehyde, acetone, benzaldehyde and 3,4,5-trimethoxybenzaldehyde. Every protein in 30S and 50S subunits was modified, although there was considerable variation in the degree of alkylation of individual proteins. A topographical classification of ribosomal proteins is presented, based on the degree of exposure of lysine residues. The data indicate that every protein of the ribosome has at least one lysine residue exposed at or near the surface of the ribonucleo-protein complex.     

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.     

Ionic Current Measurements in the Squid Giant Axon Membrane

The concepts, experiments, and interpretations of ionic current measurements after a step change of the squid axon membrane potential require the potential to be constant for the duration and the membrane area measured. An experimental approach to this ideal has been developed. Electrometer, operational, and control amplifiers produce the step potential between internal micropipette and external potential electrodes within 40 microseconds and a few millivolts. With an internal current electrode effective resistance of 2 ohm cm.², the membrane potential and current may be constant within a few millivolts and 10 per cent out to near the electrode ends. The maximum membrane current patterns of the best axons are several times larger but of the type described by Cole and analyzed by Hodgkin and Huxley when the change of potential is adequately controlled. The occasional obvious distortions are attributed to the marginal adequacy of potential control to be expected from the characteristics of the current electrodes and the axon. Improvements are expected only to increase stability and accuracy. No reason has been found either to question the qualitative characteristics of the early measurements or to so discredit the analyses made of them.     

Prevention of flowering and increasing sugar yield of sugarcane by application of ethephon (2-chloroethylphosphonic acid)

The inhibition of flowering in sugarcane by ethephon (2-chloroethylphosphonic acid) applied to experimental plots is well-documented; however, verification of its efficacy in large field trials is lacking. Large-scale field trials were established at Mauna Kea Agribusiness Company, Inc., a sugar and macadamia nut plantation located on the island of Hawaii, to determine whether flower inhibition attributed to ethephon would increase sugar yield. Summarization of results from 35 paired block experiments showed an 87% reduction in tasseling in the ethephon-treated blocks. The yield of sugarcane was increased by 7.5%, and the yield of sugar by 10%. The correlation (r ²) between the decrease in flowering and increase in cane and sugar yield was only 0.02 and 0.08%, respectively, indicating that the yield increase attributed to ethephon was not adequately explained by its effect on flowering. Paper No. 665 in the journal series of the Experiment Station, Hawaiian Sugar Planters' Association.