Utilization of Methylthio-s-Triazine for Growth of Soil Fungi

Aspergillus niger van Tieghem, Aspergillus tamarii Kita, and Aspergillus flavus Link ex Fries utilized the methylthio moiety of 2,4-bis(isopropylamino) -6-methyl-mercapto-s-triazine (prometryne) as a sulfur nutrient source. Other soil fungal isolates not affected by prometryne concentrations to 1 mg/ml culture included: Aspergillus oryzae (Ahlburg) Cohn, Curvularia lunata (Wakker) Boedijn, Trichoderma viride Persoon ex Fries, Alternaria tenuis Nees ex Corda, Penicillium funiculosum Thom, and Paecilomyces varioti Bainier.     

The dissociation of chicken erythrocyte deoxyribonucleoprotein and some properties of its partial nucleoproteins

Histones were completely dissociated from their native complex with DNA in 2.0m-sodium chloride. Histone fractions IIb, V and I were dissociated in 1.2m-sodium chloride, fractions V and I in 0.7m-sodium chloride and fraction I in 0.45m-sodium chloride. Repeated extraction of partial dRNP (deoxyribonucleoprotein) preparations with sodium chloride of the same concentration as that from which they were prepared resulted in release of histones that previously had remained associated with the DNA of the complex. Gradual removal of histones from dRNP was paralleled by an improvement in solubility, a decrease in wavelength of the u.v.-absorption minimum, and a fall in sedimentation coefficient of the remaining partial dRNP. X-ray diffraction patterns of partial dRNP preparations showed that removal of histone fractions I and V from dRNP did not destroy the super-coil structure of the dRNP, but further removal of histones did. Infrared spectra of partial dRNP preparations showed that in native dRNP histone fraction I was present in the form of extended, isolated polypeptide chains, and that the other histone fractions probably contain a helical component that lies roughly parallel to the polynucleotide chains in the double helix and an extended polypeptide component that is more nearly parallel to the DNA helix axis. An analysis of the sedimentation of partial dRNP preparations on sucrose gradients showed that native dRNP consists of DNA molecules each complexed with histone fractions of all types.     

MEMBRANE JUNCTIONS IN THE INTERMEMBRANE SPACE OF MITOCHONDRIA FROM MAMMALIAN TISSUES

There have been several reports describing paracrystalline arrays in the intermembrane space of mitochondria. On closer inspection these structures appear to be junctions of two adjoining membranes. There are two types. They can be formed between the outer and inner mitochondrial membranes (designated outer-inner membrane junctions) or between two cristal membranes (intercristal membrane junctions). In rat heart, adjoining membranes appeared associated via a central dense midline approximately 30 Å wide. In rat kidney, the junction had a ladder-like appearance with electron-dense "bridges" approximately 80 Å wide, spaced 130 Å apart, connecting the adjoining membranes. We have investigated the conditions which favor the visualization of such structures in mitochondria. Heart mitochondria isolated rapidly from fresh tissue (within 30 min of death) contain membrane junctions in approximately 10–15% of the cross sections. This would indicate that the percentage of membrane junctions in the entire mitochondrion is far greater. Mitochondria isolated from heart tissue which was stored for 1 h at 0°–4°C showed an increased number of membrane junctions, so that 80% of the mitochondrial cross sections show membrane junctions. No membrane junctions are observed in mitochondria in rapidly fixed fresh tissue or in mitochondria isolated from tissue disrupted in fixative. Thus, the visualization of junctions in the intermembrane space of mitochondria appears to be dependent upon the storage of tissue after death. Membrane junctions can also be observed in mitochondria from other stored tissues such as skeletal muscle, kidney, and interstitial cells from large and small intestine. In each case, no such junctions are observed in these tissues when they are fixed immediately after removal from the animal. It would appear that most studies in the literature in which isolated mitochondria from tissues such as heart or kidney were used were carried out on mitochondria which contained membrane junctions. The presence of such structures does not significantly affect normal mitochondrial function in terms of respiratory control and oxidative phosphorylation.     

Restriction of lambda trp bacteriophages by Escherichia coli K

trp-transducing derivatives of phage λ have been used to study Escherichia coli K specific restriction in vivo. The expression of the trp genes from unmodified phages during infection of a rec⁺, restricting host is eliminated by restriction. In a K-restricting recB,C host, where degradation of restricted phage DNA is prevented, expression of the trp genes is little affected by the presence of a single unmodified, K-restriction recognition site, even when that site is within the trpE gene. RI restriction, in contrast to K restriction, prevents trp gene expression in a recB,C host when the restriction target is between the trp genes and the relevant promoter. The presence of two K-restriction recognition sites in a λtrp phage can have a marked effect on trp gene expression. This effect can be interpreted as the result of preferential breakage between the two restriction recognition sites. We conclude that K restriction does not break susceptible DNA at, or even preferentially near, a restriction recognition sequence.     

Nucleotide sequences at the sites of action of the deoxyribonucleic acid modification enzyme of bacteriophage P1

Labelled oligonucleotides have been fractionated from DNAase digests of phage λ DNA that had been methylated with the phage P1 modification enzyme and S-[methyl-¹⁴C]adenosyl-l-methionine. The longest sequences established are the tetranucleotides pG-ǎ?-T-C4 and p?-T-C-T, which, together with the other sequences determined, particularly pA-G-?, show that the modification enzyme, M.EcoP1, methylates adenine residues within defined sequences and suggest that the oligonucleotide sequence recognized by this enzyme is the hexanucleotide pA-G-A-T-C-T. The duplex formed by base-pairing this hexanucleotide with its complementary sequence resembles the recognition sequence for several restriction enzymes in being bisected by an axis of 2-fold rotational symmetry.