The nucleotide sequences of barley cytoplasmic glutamate transfer RNAs and structural features essential for formation of δ-aminolevulinic acid

In chloroplasts and a number of prokaryotes, -aminolevulinic acid (ALA), the universal precursor of porphyrins, is synthesized by a multistep enzymatic pathway with glutamyl-tRNA^Glu as an intermediate. The ALA synthesizing system from barley chloroplasts is highly specific in its tRNA requirement for chloroplast tRNA^Glu; a number of other Glu-tRNAs are inactive in ALA formation although they can be glutamylated by chloroplast aminoacyl-tRNA synthetases. In order to obtain more information about the structural features defining the ability of a tRNA to be recognized by the ALA synthesizing enzymes, we purified and sequenced two cytoplasmic tRNA^Glu species from barley embryos which are inactive in ALA synthesis. By using glutamylated tRNAs as a substrate for the overall reaction, we showed that Glu-tRNA reductase is the enzyme responsible for tRNA discrimination.     

Tetracycline production byStreptomyces aureofaciens: the time lag of production

Summary The exact time course of phosphate consumption in a tetracycline production byStreptomyces aureofaciens has been determined. The data have been compared with model simulations according to a model proposed by Votruba et al. (1984). This led to a revision of his equation for the rate of phosphate consumption and to the proposal that phosphate is consumed proportionally to the growth rate. In contradiction to the model simulations it was found that the length of the time lag of the production is independent of the initial phosphate concentration. While the model explains the time lag through inhibition of the production by phosphate, the measured data show that there must be another or an additional reason for the lag. Simultaneously with the start of the production the organism changes from an organic substrate to ammonia as nitrogen source.All experiments have been carried out in a bubble column of 651 working volume as fed batch fermentation. An autoanalyzer and a HPLC was coupled to the reactor for automatic measurement of phosphate, ammonia, sucrose and products in short intervals. Composition of the outlet gas, pH, pO₂, temperature and weight of the substrate flasks were monitored on-line.     

Indole-3-acetic Acid oxidation and crocin bleaching by horseradish peroxidase

During indoleacetic acid (IAA) oxidation by horseradish peroxidase the water soluble model polyene, crocin, is bleached. IAA-oxidation and crocin bleaching are stimulated at acidic pH as well as by the monophenol p-hydroxyacetophenone. IAA oxidation and crocin bleaching are neither influenced by catalase or superoxide dismutase nor by different OH-radical scavengers, whereas both ascorbate and propylgallate are inhibitory.     

A detailed model of the three-dimensional structure of Escherichia coli 16 S ribosomal RNA in situ in the 30 S subunit

A large body of intra-RNA and RNA-protein crosslinking data, obtained in this laboratory, was used to fold the phylogenetically and experimentally established secondary structure of Escherichia coli 16 S RNA into a three-dimensional model. All the crosslinks were induced in intact 30 S subunits (or in some cases in growing E. coli cells), and the sites of crosslinking were precisely localized on the RNA by oligonucleotide analysis. The RNA-protein crosslinking data (including 28 sites, and involving 13 of the 21 30S ribosomal were used to relate the RNA structure to the distribution of the proteins as determined by neutron scattering. The three-dimensional model of the 16 S RNA has overall dimensions of 220 A x 140 A x 90 A, in good agreement with electron microscopic estimates for the 30 S subunit. The shape of the model is also recognizably the same as that seen in electron micrographs, and the positions in the model of bases localized on the 30 S subunit by immunoelectron microscopy (the 5' and 3' termini, the m7G and m6(2)A residues, and C-1400) correspond closely to their experimentally observed positions. The distances between the RNA-protein crosslink sites in the model correlate well with the distances between protein centres of mass obtained by neutron scattering, only two out of 66 distances falling outside the expected tolerance limits. These two distances both involve protein S13, a protein noted for its anomalous behaviour. A comparison with other experimental information not specifically used in deriving the model shows that it fits well with published data on RNA-protein binding sites, mutation sites on the RNA causing resistance to antibiotics, tertiary interactions in the RNA, and a potential secondary structural "switch". Of the sites on 16 S RNA that have been found to be accessible to chemical modification in the 30 S subunit, 87% are at obviously exposed positions in the model. In contrast, 70% of the sites corresponding to positions that have ribose 2'-O-methylations in the eukaryotic 18 S RNA from Xenopus laevis are at non-exposed (i.e. internal) positions in the model. All nine of the modified bases in the E. coli 16 S RNA itself show a remarkable distribution, in that they form a "necklace" in one plane around the "throat" of the subunit. Insertions in eukaryotic 18 S RNA, and corresponding deletions in chloroplast or mammalian mitochondrial ribosomal RNA relative to E. coli 16 S RNA represent distinct sub-domains in the structure.(ABSTRACT TRUNCATED AT 400 WORDS)     

Seasonal succession of ciliates in lake constance

We found a recurrent seasonal pattern in abundance and composition of planktonic ciliates in Lake Constance, FRG, over a three-year period. Abundance peaks occurred in early spring and summer/autumn, while ciliate numbers were low in late spring (clear-water phase) and winter. Prostomatida and Oligotrichida dominated in early spring. They responded immediately to the phytoplankton spring bloom, while Haptorida, Peritrichida, and large Scuticociliatida (Histiobalantium) were delayed by 1 to 2 weeks. The spring community broke down at the onset of the clear-water phase.Pelagohalteria viridis containing symbiontic algae appeared shortly after this event. A highly diverse community was recorded in summer/autumn. Peritrichida, small Oligotrichida, and large Scuticociliatida reached their maxima during this season. Small Scuticociliatida were rare throughout the year and contributed moderately to total ciliate numbers only during the cold season. The observed seasonal sequence of pelagic ciliates in Lake Constance is discussed in relation to simultaneously collected data on potential food organisms and grazers.     

Morphology and structural organization of Haller's organ during postembryonic development ofArgas (Persicargas) walkerae (Ixodoidea: Argasidae)

Scanning-electron-microscopic investigations of Haller's organ in larvae, nymphs I, II, III and IV, and male and female adultArgas (Persicargas) walkerae ticks showed that morphology and structural organization change during postembryonic development. Stage-dependent differences existed regarding setal numbers of the anterior pit as well as formation and reticulation of cuticular projections in the capsule cavity. The anterior pit increased in size in the course of postembryonic development. It contained only seven setae in larvae, one conical, setiform and grooved seta each as well as two porose and fine setae. Nymphs I, II, III and IV and adult ticks had equal numbers of setae; however, one additional unilaterally serrate and grooved seta each were present. Setal length increased continuously during postembryonic development and attained maximum values in adult ticks. The capsule consisted of roof and cavity and was located distinctly lateral in larvae, slightly lateral in nymphs I and II, and in all other stages directly on the longitudinal axis of tarsus. The capsule roof showed a reticular structure. The slit-like main aperture was located peripherally and arranged transversally to the longitudinal axis of tarsus I in larvae. Nymphs and adult ticks had a central, circular main aperture. Stage-dependent cuticular projections of varying form protruded into the capsule cavity. Larvae had only single, free-standing projections which ramified slightly and communicated with each other. Projections were more heavily reticulated in nymphs I and II. In nymphs III and IV as well as male and female adult ticks, a long centrally situated tube of reticular appearance was seen, which was supported by a large number of radially organized and interlocking pillars and communicated with the capsule roof. In all tick stages there were always four porose setae present, arranged on the capsule floor.     

Gramicidin in chromatophores of Rhodobacter sphaeroides

Chromatophores of Rhodobacter sphaeroides were excited with light flashes to generate a transmembrane electrical potential difference. The electric relaxation was measured by electrochromic absorption changes as a function of added gramicidin. At low gramicidin/bacteriochlorophyll (BChl) molar ratios the decay of the electrochromic absorption changes showed a biphasic behaviour, with a fast phase relaxing at some s, and a slow phase relaxing at more than 100 ms. This was attributable to a mixture of vesicles containing gramicidin dimers with others containing none. The concentration dependence of this effect was linear. This implied full dimerization of gramicidin. The data were interpreted to yield an average bacteriochlorophyll content per chromatophore of 770(±150) and the conductance of a single gramicidin dimer in the chromatophore membrane of 15(±4) pS (in about 115 mM KCl).Abbreviations BChl Bacteriochlorphyll - tricine N-Tris[hydroxymethyllmethylglycine Offprint requests to: W. Junge     

Formation of acetic acid from cellulosic substrates byFusarium oxysporum

Summary Four strains of Fusarium oxysporum and a strain of Monilia brunnae were screened for their ability to convert cellulosic substrates into ethanol/acetic acid. These strains were found to utilize cellulose and produce extracellular cellulases. However, only F. oxysporum 841 was found to convert glucose, xylose, and cellulose into ethanol and acetic acid as major end-products under microaerobic conditions. Acetic acid at a level of 4.7 g/l resulted in a single-step process on potato pulp medium, indicating the potential of the strain for converting cellulosic substrates into acetic acid. Offprint requests to: K. Schügerl