Valanginian to Aptian calcareous nannofossil stratigraphy and correlation with the upper M-sequence magnetic anomalies

Calcareous nannofossil stratigraphy has been investigated in Lower Cretaceous Italian sections at Gorgo a Cerbara, Presale and Frontale (all in the Umbrian Apennines) and at Cismon (Southern Alps). A modified sample preparation technique has allowed a thorough stratigraphic study of the well-lithified Maiolica limestone and although nannofossil preservation is generally quite poor, the major Valanginian to Aptian marker species can be detected. Nine nannofossil events can be determined and correlated to magnetic stratigraphies previously established in these sections. Nannofossil stratigraphy confirms most magnetostratigraphic correlations made between sections and allows a more precise correlation of magnetic Chrons M-0 to M-11 with the Valanginian, Hauterivian, Barremian and Aptian stages. The results obtained differ considerably from previous timescales. Nannofossil events recorded in the various sections may be time-transgressive by as much as one magnetic chron, probably due to differential preservation.     

Isolation and characterization of an ipt gene from the Ti plasmid Bo542

Summary A 1.9 kb clone of the T-DNA region of the Agrobacterium tumefaciens Ti plasmid Bo542 which exhibited homology to the isopentenyl transferase (ipt) locus of pTiA6 was identified by low stringency DNA hybridization. Introduction of this segment of pTiBo542 DNA into cells of Nicotiana tabacum or N. glauca caused tumor formation in vivo, and allowed hormone independent growth in vitro. Furthermore, this DNA segment complemented ipt mutant strains of A. tumefaciens, restoring their ability to cause tumors on Kalanchöe leaves and tomato stems. The complete DNA sequence of this segment has been determined, revealing an open reading frame homologous to other known Agrobacterium ipt genes.     

Computational experience with an algorithm for tetrangle inequality bound smoothing

An important component of computer programs for determining the solution conformation of proteins and other flexible molecules from nuclear magnetic resonance data are the so-called “bound smoothing algorithms”, which compute lower and upper limits on the values of all the interatomic distances from the relatively sparse set which can usually be measured experimentally. To date, the only methods efficient enough for use in large problems take account of only the triangle inequality, but an appreciable improvement in the precision of the limits is possible if the algebraic relations between the distances among each quadruple of atoms are also considered. The goal of this paper is to use a recently improved algorithm for computing these “tetrangle inequality limits” to determine just how much improvement really is possible, given the types of experimental data that are usually available.     

Interrelationship of kernel water activity,soil temperature,maturity, and phytoalexin production in preharvest aflatoxin contamination of drought-stressed peanuts

Samples of Florunner peanuts were collected throughout a period of late-season drought stress with mean geocarposphere temperatures of 29 and 25 °C, and determinations of maturity, kernel water activity (a_w), percent moisture, capacity for phytoalexin production, and aflatoxin contamination were made. Results showed an association between the loss of the capacity of kernels to produce phytoalexins and the appearance of aflatoxin contamination. Kernel a_w appeared to be the most important factor controlling the capacity of kernels to produce phytoalexins. Mature peanuts possessed additional resistance to contamination that could not be attributed solely to phytoalexin production. Kernel moisture loss was accelerated in the 29 °C treatment compared to the 25 °C treatment, and data indicated that the higher soil temperature also favored growth and aflatoxin production by Aspergillus flavus in peanuts susceptible to contamination.Mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by the U.S. Department of Agriculture and does not imply its approval to the exclusion of other products that may also be suitable.     

DNA nucleotide sequence analysis of the immediate-early gene of pseudorabies virus.

The complete DNA sequence coding for the immediate-early protein (IE180) of pseudorabies virus was determined. The coding region of IE180 is 4380 nucleotides for 1460 amino acid residues. G+C content of the non-coding portion of the IE gene is 70.3% while the G+C content of the coding portion is considerably higher at 80.1%. Correspondingly, codons consisting mainly of Gs and Cs are favoured. Clusters of amino acid homologies are observed among IE180 of pseudorabies virus, ICP4 of herpes simplex virus type-1 and IE140 of varicella-zoster virus, and are organized similarly in all three polypeptides. Functions exhibited by IE180 are assigned, tentatively, to structural domains of the molecule by analogy to the HSV-1 ICP4 polypeptide.     

Vitamin K-dependent carboxylase: influence of the "propeptide" region on enzyme activity

The liver microsomal vitamin K-dependent carboxylase catalyzes the post-translational conversion of specific glutamyl to gamma-carboxyglutamyl (Gla) residues in precursor forms of a limited number of proteins. These proteins contain an amino-terminal extension (propeptide) that is presumed to serve as an enzyme recognition site to assure their normal processing. The free, noncovalently bound propeptide has also been shown to stimulate the in vitro activity of this enzyme. This peptide has now been shown to lower the app Km of a low-molecular-weight Glu site substrate while having no influence on the app Km of the other substrates, vitamin KH2, O2, and CO2/HCO3-. Propeptide addition was shown to have no influence on the ratio of the two products of the enzyme, Gla and vitamin K-2,3-epoxide. Stimulation of carboxylase activity by the propeptide from human factor X was observed in a number of rat tissues and in the liver of a number of different species. Stability of the enzyme in crude microsomal preparations was greatly enhanced by the presence of propeptide. These observations are consistent with the hypothesis that this region of the protein substrates for the carboxylase not only serves an enzyme recognition or docking function but also modulates the activity of the enzyme by altering the affinity for one of its substrates.     

Augmentation of inorganic pyrophosphate elaboration in cartilage by serum factors

The disordered production of inorganic pyrophosphate (PPi) by articular cartilage is thought to have an important role in the pathogenesis of calcium pyrophosphate dihydrate deposition disease and perhaps osteoarthritis. We have previously shown that fetal calf serum added to the culture media of porcine articular cartilage explants increases the elaboration of PPi into the ambient media. We have examined this PPi stimulatory activity by studying the effects of adult human serum (HS), serum derived from adult human plasma (HP), and an acid-alcohol extract of human platelets (PE) on PPi production in cartilage organ culture. Ten percent HS produces a 1.4-fold increase in PPi production after 48 h of culture, while cartilage incubated in media containing 10% HP produces no more PPi than that incubated in media alone. PE stimulates a mean 2-fold increase in PPi production at 48 h in the presence of low concentrations of HP, and has no effect alone. It does not appear to up-regulate the activity of the ectoenzyme nucleoside triphosphate pyrophosphohydrolase (NTPPPH), nor does it promote the release of enzyme substrate into the extracellular space. Cartilage exposed to 0.5% HP and PE has 1.51 +/- 0.36 units of NTPPPH activity whereas cartilage exposed to 0.5% HP alone has 1.52 +/- 0.41 units of enzyme activity. PE does not increase the release of [14C]adenine-labeled compounds into the media. Approximately 13% of soluble 14C counts was found in the media of chondrocytes treated with PE while 18% of counts was released in the presence of HP alone. We have demonstrated a factor or factors present in FCS, HS, and an acid-ethanol extract of human platelets which represent(s) the first known physiologic modulators of PPi production in articular cartilage and may increase PPi production without affecting NTPPPH activity.     

NMR studies of differences in the conformations and dynamics of ligand complexes formed with mutant dihydrofolate reductases

Two mutants of Lactobacillus casei dihydrofolate reductase, Trp 21----Leu and Asp 26----Glu, have been prepared by using site-directed mutagenesis methods, and their ligand binding and structural properties have been compared with those of the wild-type enzyme. 1H, 13C, and 31P NMR studies have been carried out to characterize the structural changes in the complexes of the mutant and wild-type enzymes. Replacement of the conserved Trp 21 by a Leu residue causes a decrease in activity of the enzyme and reduces the NADPH binding constant by a factor of 400. The binding of substrates and substrate analogues is only slightly affected. 1H NMR studies of the Trp 21----Leu enzyme complexes have confirmed the original resonance assignments for Trp 21. In complexes formed with methotrexate and the mutant enzyme, the results indicate some small changes in conformation occurring as much as 14 A away from the site of substitution. For the enzyme-NADPH complexes, the chemical shifts of nuclei in the bound coenzyme indicate that the nicotinamide ring binds differently in complexes with the mutant and the wild-type enzyme. There are complexes where the wild-type enzyme has been shown to exist in solution as a mixture of conformations, and studies on the corresponding complexes with the Trp 21----Leu mutant indicate that the delicately poised equilibria can be perturbed. For example, in the case of the ternary complex formed between enzyme, trimethoprim, and NADP+, two almost equally populated conformations (forms I and II) are seen with the wild-type enzyme but only form II (the one in which the nicotinamide ring of the coenzyme is extended away from the enzyme structure and into the solvent) is observed for the mutant enzyme complex. It appears that the Trp 21----Leu substitution has a major effect on the binding of the nicotinamide ring of the coenzyme. For the Asp 26----Glu enzyme there is a change in the bound conformation of the substrate folate. Further indications that some conformational adjustments are required to allow the carboxylate of Glu 26 to bind effectively to the N1 proton of inhibitors such as methotrexate and trimethoprim come from the observation of a change in the dynamics of the bound trimethoprim molecule as seen from the increased rate of the flipping of the 13C-labeled benzyl ring and the increased rate of the N1-H bond breaking.