Assignment of imino proton spectra of yeast phenylalanine transfer ribonucleic acid

Yeast tRNAPhe has been studied by using proton NMR and nuclear Overhauser effect (NOE) with deuterium substitution. Direct NOE evidence is presented for assignment of imino resonances of 23 of 27 base pairs in this tRNA. Other indirect evidence is presented for tentative assignment of four other base pairs. Almost total assignment also has been made of the important noninternally bonded imino protons and tertiary interactions (however, G18-psi 55 remains unassigned). The most surprising result has been identification of GC11 at -13.68 ppm; this is the first time a GC base pair has been identified so far downfield. This peak (GC11) is also identified as the resonance of the unique imino proton that exchanges in a time of more than 1 day, as previously described. These identifications of imino proton resonances made it possible to reinterpret the proton solvent exchange rate data previously published on this tRNA and understand them better. The assignments of resonances should pave the way for more detailed solution study of this tRNA and its interaction with biologically relevant molecules.     

Glycerol catabolite regulation of d-cycloserine production in Streptomyces garyphalus

A fluorescent pigment was isolated from the culture fluid of Methanobacterium thermoautotrophicum strain H. This pigment was shown to be 7,8-didemethyl-8-hydroxy-5-deazariboflavin by various spectroscopic and chromatographic techniques. This compound was previously described as the FO acid hydrolysis fragment of coenzyme F₄₂₀. On the basis of the time of appearance of the pigment in the course of fermentation, it is suggested that this substance may be an over-produced biosynthetic precursor of F₄₂₀.     

Chromosome Transfer and Recombinant Formation with Deoxyribonucleic Acid Temperature-Sensitive Strains of Escherichia coli

Haploid recombinant yield is reduced in matings conducted at 42.5 C between deoxyribonucleic acid (DNA) temperature-sensitive [dna⁻(TS)] recipients unable to synthesize DNA at 42.5 C and any of the three major donor types (Hfr, F⁺, F′) of Escherichia coli. No such reduction is observed in matings conducted at 42.5 C when the dna⁻(TS) mutation is in the donor parent. Evidence is presented which indicates that chromosome transfer from donors to recipients unable to replicate DNA at 42.5 C during vegetative growth occurs at normal frequencies when the mating is conducted at 42.5 C. It is concluded that some stage in haploid recombinant formation is adversely affected in dna⁻(TS) recipients mated at the temperature restrictive for DNA synthesis.     

Isolation of two pure polysaccharides from the hemicellulose of slash pine (Pinus elliottii)

Two pure, acidic polysaccharides have been isolated from the hemicellulose of slash pine in yields of 1–2% and 4–5%. Their properties are compared, and the structure of one of them has been investigated by methylation analysis. The results indicate that the glycan is a β-D-(1→4)-linked xylan chain with many branch points. 4-O-Methyl-D-glucopyranosyluronic acid, L-arabinofuranose, and D-xylopyranose residues occur as non-reducing end groups. The uronic acid occurs as single-unit attachments to the main chain. Some of the D-xylose residues in the polysaccharide are doubly branched. The total hemicellulose components of the wood probably represent a complex mixture of chemical types, from which the two pure fractions described above may be separated fortuitously by careful, fractional precipitation.     

Nickel Substitution for Calcium in Excitation-Contraction Coupling of Skeletal Muscle

In 1962 Frank (22) reported that the addition of any one of a number of divalent cations, including Ni, to a Ca-free Ringer solution prevented the rapid loss of contractility seen in the absence of external Ca. To investigate further the Ni-Ca substitution, studies were made of ⁴⁵Ca and ⁶³Ni exchange during contraction and at rest using frog striated muscle. In contrast to ⁴⁵Ca, it was found that there is no increase of ⁶³Ni uptake associated with a K contracture of the sartorius muscle. The rates of loss of ⁶³Ni and ⁴⁵Ca from resting toe muscles previously bathed in the respective radioisotopes are not significantly different. Resting and action potentials, after 1 hr in a Ringer solution with Ni replacing Ca, closely resemble these potentials in normal Ca-Ringer's solution. Studies on the syneresis of isolated myofibrils indicate that Ni cannot replace Ca in activating this reaction. It is suggested that Ca is required for at least two steps in E-C coupling: one is the spread of excitation at the sarcolemma and transverse tubular system; the second is the activation of actomyosin ATPase. Conceivably Ni can substitute for Ca in the former but not in the latter.     

STUDIES OF NECROTIC LESIONS IN CORN STALKS

Littlefield , Larry J., and Roy D. Wilcoxson . (U. Minnesota, St. Paul.) Studies of necrotic lesions in corn stalks . Amer. Jour. Bot. 49(10): 1072–1078. Illus. 1962.—In 3-day-old necrotic lesions in corn stalks caused by Fusarium graminearum, ground parenchyma cells were discolored and small amounts of a dark substance were present in the cells. The walls of phloem cells were also slightly discolored and a small amount of dark substance was present in the xylem cells. In older lesions the discoloration of parenchyma and phloem cells was more intense; many of the cells contained occluding substances; many phloem protoplasts collapsed, and xylem cells were partially to completely occluded. The occluding substance filling the cells appeared to be translocated from the lesion into the vessel elements extending beyond the lesion so that the bundles appeared as long, dark streaks in the stalk. The occluding substance in xylem, but not in phloem or parenchyma, stained with ruthenium red, a result indicating presence of pectin. Pectinase, however, did not remove the occluding substance. The pectinase dissolved the parenchyma cells in healthy tissues but not in the necrotic lesions. Necrosis in naturally infected plants began as small lesions, but the parenchyma cells quickly dissolved leaving the vascular bundles free of ground parenchyma. No occlusions were found in the central vascular system; a few xylem cells in the peripheral vascular system were occluded with the same substance observed in artificially inoculated plants. Phloem was entirely destroyed by the pathogen. The necrosis prevented upward movement of dye solution in the stalk, but did not measurably affect transpiration, probably because the lesions were not large. Yield was reduced in plants when lesions involved more than 50% of the tissue in inoculated internodes. Smaller lesions had no effect on yield.