Lack of in vivo transcription of Acetabularia mediterranea 1175 bp ctDNA fragment homologous to the Drosophila per locus.

The period (per) locus of Drosophila melanogaster has a fundamental role in the expression of biological rhythms. A DNA sequence homologous to a short region of the Drosophila per locus was detected in the chloroplast of Acetabularia mediterranea. A 1175 bp DNA fragment containing the sequence was used as a probe in 'Northern' hybridization experiments. It was found that this DNA was not transcribed or only marginally transcribed in A. mediterranea, at least at the developmental stage just prior to cap formation. It seems that the 1175 bp ctDNA fragment is not involved in the Acetabularia biological rhythm mechanism.     

The repair of large DNA adducts in mammalian cells.

This paper describes experiments involving the measurement of DNA damage and repair after treatment with 4-nitroquinoline 1-oxide (4NQO) or aflatoxin B1 (AFB1) epoxide in a number of mammalian cell cultures primarily associated with defects in the excision repair of UV-induced DNA damage. The results with transformed derivatives of XP cells belonging to different complementation groups showed that the extent of repair of 4NQO adducts at the N2 or C8 of guanosine did not correlate to the extent of repair reported by others after UV-irradiation. An examination of 4NQO repair in rodent UV-sensitive cell lines from different ERCC groups indicated that again there was little correlation between the extent of 4NQO and UV repair. However, regardless of complementation group those mutants that were defective in the repair of pyrimidine dimers and 6,4-photoproducts did exhibit a reduced ability to repair the 4NQO N2 guanosine adduct, whereas those mutants defective in pyrimidine dimer repair alone were able to repair this lesion as normal. In all of these cell lines there was a normal capacity to repair the 4NQO C8 guanosine adduct. Less extensive experiments involving AFB1 epoxide showed an XPC-transformed cell line was able to repair 40% of lesions after 6 h, whereas only 20% of repair is seen after UV. The rodent mutant V-C4 which belongs to the same ionising radiation group as irs2, was partially defective in repairing AFB1-induced damage. These experiments highlight the fact that although there are many commonalities between the repair of UV damages and lesions classed as large DNA adducts differences clearly exist, the most striking example here being the repair of the C8 guanosine 4NQO adduct which rarely correlates with a defect in UV repair.     

Iron-molybdenum cofactor from nitrogenase. Modified extraction methods as probes for composition

Five modifications of the preparative procedure for isolating iron-molybdenum cofactor (FeMoco) from the molybdenum-iron (MoFe) protein of Azotobacter vinelandii nitrogenase have been developed. This variety of isolation methods has established that no single component of the original isolation protocol, i.e. Tris, Cl-, citrate, HPO4(2-), N,N-dimethylformamide, and N-methylformamide, is essential for the effective isolation and/or structural stability of FeMoco, although any of them may act as ligands to FeMoco when present. The acid-bse status (effective pH) of the extracting solvent is a key adjustable parameter in the isolation procedure. The new procedures produced FeMoco with yields, metal analysis, charge, EPR spectrum, and specific activity (after reconstituting crude extracts from A. vinelandii UW45 mutant cells) essentially identical with FeMoco isolated by the original procedure. After purification, FeMoco apparently contains molybdenum, iron, and sulfide in a 1:7:4 ratio with N-methylformamide as a ligand but no amino acid residues, common sugars, coenzyme A, or lipoic acid. Reaction with o-phenanthroline allows quantitation of both adventitious and FeMoco-associated iron. Correlations of total activity after UW45 reconstitution with molybdenum, total iron, and o-phenanthroline-resistant iron contents show that only the last gives a consistent relationship of 35 +/- 5 nmol of C2H4/min/ng atom of Fe. Both o-phenanthroline and EDTA interact with FeMoco to abolish its EPR signal in reactions reversible by additions of Fe2+ or Zn2+, respectively. These and related reactions point against the presence of an endogenous organic component in FeMoco and toward the presence of exogenous ligands and imply a relatively labile coordination sphere whose nature may be determinable by a systematic investigation.     

Decrease of estrogen receptors induced by 17 beta-estradiol and progesterone in cultured rabbit endometrial cells

A whole cell technique to measure estradiol receptors in cultured rabbit endometrial cells is described. The estradiol receptors measured appear to be composed of at least two components: one component has high affinity but low capacity, while the other component has low affinity but high capacity. Using the assay, the effects of estradiol and progesterone pretreatment were examined on the estradiol receptor levels. It was found that both of the hormones decreased the number of estrogen receptors in the cultured cells. The finding that estradiol decreased its own receptors was unexpected and its possible relevance is discussed.     

Purification of bull sperm hyaluronidase by concanavalin-A affinity chromatography.

A new method for obtaining highly purified hyaluronidase (hyaluronate glycanohydrolase EC 3.2.1.25) in high yield is described. Bull seminal plasma was fractionated with (NH4)2 SO4 and the 30 to 65% saturation fractions were applied to a DEAE-cellulose column. The first protein peak contained hyaluronidase, beta-N-acetylglucosaminidase and beta-glucuronidase. The latter two enzymes were separated by gel filtration on Sephadex G-200. The hyaluronidase was further purified by a Concanavalin-A Sepharose 4B affinity column. By gradient elution with alpha-methyl-D-glucoside a fraction which had a specific activity of 1998 units/mg protein (57 942 National Formulary Standard units/mg protein) was obtained. The highly purified enzyme showed one major protein band on acrylamide gel electrophoresis at pH 4.3. The purified hyaluronidase did not show any beta-glucuronidase or beta-N-acetylglucosaminidase activities. The percent yield of purified hyaluronidase calculated on the basis of total activity was ten times higher than by any pervious method [Yang, C.H. and Srivastava, P.N. (1975) J. Biol. Chem. 250, 79-83].     

Inhibition of bull and rabbit sperm enzymes by alpha-chlorohydrin.

High concentrations of alpha-chlorohydrin were found to inhibit hyaluronidase, beta-glucuronidase, and aryl sulphatases in bull and rabbit spermatozoa, but not acrosin and neuraminidase. Preincubation of the enzyme and alpha-chlorohydrin was essential to achieve the maximum inhibition which was irreversible.     

Environmental filtering rather than dispersal limitation dominated plant community assembly in the Zoige Plateau

Identifying the mechanisms that underlie the assembly of plant communities is critical to the conservation of terrestrial biodiversity. However, it is seldom measured or quantified how much deterministic versus stochastic processes contribute to community assembly in alpine meadows. Here, we measured the decay in community similarity with spatial and environmental distance in the Zoige Plateau. Furthermore, we used redundancy analysis (RDA) to divide the variations in the relative abundance of plant families into four components to assess the effects of environmental and spatial. Species assemblage similarity liner declined with geographical distance (p < .001, R ² = .6388), and it decreased significantly with increasing distance of total phosphorus (TP), alkali‐hydrolyzable nitrogen (AN), available potassium (AK), nitrate nitrogen (NO₃ ⁺–N), and ammonia nitrogen (NH₄ ⁺–N). Environmental and spatial variables jointly explained a large proportion (55.2%) of the variation in the relative abundance of plant families. Environmental variables accounted for 13.1% of the total variation, whereas spatial variables accounted for 11.4%, perhaps due to the pronounced abiotic gradients in the alpine areas. Our study highlights the mechanism of plant community assembly in the alpine ecosystem, where environmental filtering plays a more important role than dispersal limitation. In addition, a reasonably controlled abundance of Compositae (the family with the highest niche breadth and large niche overlap value with Gramineae and Cyperaceae) was expected to maintain sustainable development in pastoral production. These results suggest that management measures should be developed with the goal of improving or maintaining suitable local environmental conditions.