Horizontal Escape of the Novel Tc1-Like Lepidopteran Transposon TCp3.2 into Cydia pomonella Granulovirus

We characterized an insertion mutant of the baculovirus Cydia pomonella granulovirus (CpGV), which contained a transposable element of 3.2 kb. This transposon, termed TCp3.2, has unusually long inverted terminal repeats (ITRs) of 756 bp and encodes a defective gene for a putative transposase. Amino acid sequence comparison of the defective transposase gene revealed a distant relationship to a putative transposon in Caenorhabditis elegans which also shares some similarity of the ITRs. Maximum parsimony analysis of the predicted amino acid sequences of Tc1- and mariner-like transposases available from the GenBank data base grouped TCp3.2 within the superfamily of Tc1-like transposons. DNA hybridization indicated that TCp3.2 originated from the genome of Cydia pomonella, which is the natural host of CpGV, and is present in less than 10 copies in the C. pomonella genome. The transposon TCp3.2 most likely was inserted into the viral genome during infection of host larvae. TCp3.2 and the recently characterized Tc1-like transposon TC14.7 (Jehle et al. 1995), which was also found in a CpGV mutant, represent a new family of transposons found in baculovirus genomes. The occasional horizontal escape of different types of host transposons into baculovirus genomes evokes the question about the possible role of baculoviruses as an interspecies vector in the horizontal transmission of insect transposons. Received: 27 February 1997 / Accepted: 16 May 1997     

Glutamate dehydrogenase of the unicellular green alga Scenedesmus acutus

The coenzyme-non-specific glutamate dehydrogenase (EC 1.4.1.3) from Scenedesmus acutus in inhibited by p-hydroxymercuribenzoate only in the deamination reaction. From this result and from its stability in the presence of urea it is concluded that this enzyme exhibits and equilibrium between three conformations: aminating and deaminating conformations induced by NADH-2-oxoglutarate and NAD⁺-glutamate, respectively, and the “native” conformation in the absence of substrates.     

C(24)- and C(23)-oxidation, converging pathways of intestinal 1,25-dihydroxyvitamin D3 metabolism: identification of 24-keto-1,23,25-trihydroxyvitamin D3

24-Keto-1,23,25-trihydroxyvitamin D3 has been identified as a major 1,25-dihydroxyvitamin D3 metabolite, produced by intestinal mucosa cells isolated from rats dosed chronically with 1,25-dihydroxyvitamin D3. The identification was based on ultraviolet absorbance spectroscopy, mass spectroscopy, and chemical derivatization. The pathway of biosynthesis proceeded through 1,24,25-trihydroxyvitamin D3 and 24-keto-1,25-dihydroxyvitamin D3, which are physiological metabolites of 1,25-dihydroxyvitamin D3. Previous work [Napoli, J. L., Pramanik, B. C., Royal, P. M., Reinhardt, T. A., & Horst, R. L. (1983) J. Biol. Chem. 258, 9100-9107] had shown that the amount of 24-keto-1,23,25-trihydroxyvitamin D3 in intestine in vivo, relative to its C(24)-oxidized precursors, is enhanced by chronically dosing rats with 1,25-dihydroxyvitamin D3. These results establish the C(24)-oxidation pathway as a predominant route of intestinal 1,25-dihydroxyvitamin D3 metabolism under physiological conditions and indicate that treatment of the rat with exogenous 1,25-dihydroxyvitamin D3 causes expression of C(23)-hydroxylase activity, which uses C(24)-oxidized 1,25-dihydroxyvitamin D3 metabolites as substrates.     

Ependymal and neuronal specializations in the lateral ventricle of the Pekin duck,Anas platyrhynchos

Summary The lateral ventricles of the Pekin duck, Anas platyrhynchos, display characteristic ependymal and hypendymal specializations. Adjacent to the nucleus accumbens and the basal pole of the lateral septum the ventricular surface shows a highly folded pattern either with protrusions into the ventricular lumen or deep invaginations into the brain tissue. These medial and basal ependymal folds are found exclusively in a circumscribed region extending over a range of 600 m in the rostrocaudal direction. Ependymal folds occurring in the lateral wall of the ventricles were traced up to the level of the interventricular foramen. Numerous capillaries are observed in the subependymal layer of these folds.By means of immunocytochemistry with antibodies against chicken vasoactive intestinal polypeptide (VIP) an aggregation of classical cerebrospinal fluid-contacting neurons is shown in the region of the nucleus accumbens and the lateral septum. These neurons are closely related to the ependymal folds. Additional VIP-immunoreactive neurons are scattered in deeper layers of the lateral septum and the nucleus accumbens. The latter are richly innervated by VIP-immunoreactive nerve fibers.The results of the present study are discussed with particular reference to the hypothesis of Kuenzel and van Tienhoven (1982) that ependymal specializations demonstrated in the lateral ventricles of the domestic fowl might represent a new circumventricular organ (lateral septal organ).The authors are greatly indebted to Professor A. Oksche for stimulating discussionsSupported by the Deutsche Forschungsgemeinschaft (Ko 758/2-2; 2-3) and the P. Carl Petersen Foundation     

Different isoforms of an apoprotein (apolipophorin III) associate with lipoproteins in Locusta migratoria

Insects transport lipid for flight in the form of diacylglycerol-rich low-density lipoproteins (low-density lipophorin, LDLp), which in the hemolymph are produced from high-density lipophorin (HDLp) by reversible association with several molecules of an apolipoprotein, apolipophorin III (apoLp-III, Mr approximately 18,000-20,000) during lipid loading. Two isoforms of apoLp-III (a and b) were purified both from adult Locusta migratoria migratorioides hemolymph and LDLp, which have identical apparent Mr but differ in amino acid composition, NH2-terminal amino acid sequence, and isoelectric points (5.35 +/- 0.01 for apoLp-IIIa, 5.10 +/- 0.01 for apoLp-IIIb). The NH2-terminal sequence of apoLp-IIIb is identical to the primary structure of apoLp-III deduced from cloned cDNA [Kanost et al. (1988) J. Biol. Chem. 263, 10,568-10,573], whereas the NH2-terminal sequence of apoLp-IIIa is identical to that of apoLp-IIIb but preceded by Arg-Pro-, which is the C-terminal of the putative signal peptide coded by cDNA upstream from that coding for apoLp-IIIb. The ratio apoLp-IIIa apoLp-IIIb free in hemolymph is identical to that in LDLp (5:9); since 14 molecules of apoLp-III appear to be bound in one molecule of LDLp, an average of 5 molecules of apoLp-IIIa and 9 of apoLp-IIIb are involved in formation of each LDLp particle. In vivo studies using 35S-labeled apoLp-IIIa and b demonstrate that each of the isoforms can associate with HDLp to produce LDLp reversibly; in an in vitro system, production of LDLp containing exclusively apoLp-IIIa or apoLp-IIIb demonstrates independent participation of each isoform in LDLp formation.     

Functional mechanism of water splitting photosynthesis

A personal account is given on physico-chemical aspects of photosynthesis. The article starts with the way I entered the field of photosynthesis. Then, selected results from our research group are discussed. Three methods used for functional analysis in our laboratory are described: the repetitive flash spectroscopy; the electrochromic volt- and ammeter; and the membrane energization by a battery. Our subsequent studies deal with the two photoreaction centers, the primary charge separation, the plastoquinones as a transmembrane link between the two centers and the vectorial electron- and proton pathways. The results led to a picture of the elementary functional mechanism of the molecular machinery in the thylakoid membrane. The perspective then focuses on the coupling between the electric field, protons and phosphorylation. This section is followed by our observations and analysis of the mechanism of water cleavage and its coupling with the functioning of reaction center II. Finally, information is provided on structural aspects of the two reaction centers. The article ends with a retrospect.Abbreviations ADP(ATP) adenosine di(tri)phosphate - A₀, A₁ electron carriers - Car carotenoid - Chl-a ₁ (P700) chlorophyll-a ₁ - Chl-a _II (P680) chlorophyll-a _II - Cyt cytrochrome - Fd ferredoxin - FeS iron sulphur - Fe iron - F_X, F_A, F_B FeS clusters - HA hydroxylamine - Mn manganese - NADP⁺ (TPN) nictoinamide adenine dinucleotide phosphate - PC plastocyanin - Pheo pheophytin - PQ plastoquinone - P phosphate - Q_A (Q_B) primary (secondary) plastoquinone acceptor - RC I(II) reaction center I (II) - S_{0, 1, 2, 3, 4} different states of the water splitting enzyme S - Tyr tyrosine - X,Y,Z unknown redox components This article was written at the invitation of Govindjee.     

Two types of chloride channels in hen colon epithelial cells identified by patch-clamp experiments

Summary Freshly isolated epithelial cells from hen colon were investigated using the patch-clamp technique. The aim of this investigation was to characterise the cellular conducting site for Cl^- secretion. In cell-attached mode two types of Cl^--channels were found. Both showed distinct outward rectification. The channel types differed in single channel conductances and the marked voltage dependence of the open probabilities. A low conductance Cl^--channel was observed with a mean conductance at negative holding potentials of g_-=9 pS, and of g₊=34 pS at positive potentials. This channel was predominantly open at negative potentials, corresponding to cell hyperpolarization. The second channel type observed had conductances of g_-=35 pS and g₊=77 pS, and showed increasing open probabilities with increasing holding potentials (cell depolarisation). Both channel types were blockable by the Cl^--channel blocker NPPB. These data in combination with previously published transepithelial transport data on hen colon indicate that these channels are the Cl^- secretory sites in colon epithelium.Abbreviations DNSO dimethylsulfoxide - EGTA ethyleneglycol triacetic acid - g₊, g_- single channel conductance at positive and negative voltages - HEPES N-(2-hydroxy-ethyl)piperazine-N-(2-ethane-sulfonic acid) - i single channel current - NMDG N-methyl-d-glucosamine - NPPB 5-hitro-2-(3-phenylpropylamino)-benzoate - P_o open probability - V_p holding potential     

Recurrent nonsense mutation in exon 7 of the phenylalanine hydroxylase gene

Summary A new mutation (CGA to TGA) in codon 261 of exon 7 of the phenylalanine hydroxylase gene transforms Arg²⁶¹ to a stop codon in two unrelated patients of German and Turkish origin. The different ethnic backgrounds and the different polymorphic characteristics of the two mutant alleles suggest an independent origin of the mutation. This is the second defect detected in codon 261 of the phenylalanine hydroxylase gene, a codon that thus appears to be a mutation hot spot.