No abstract

Reversible ADP-ribosylation of dinitrogenase reductase forms the basis of posttranslational regulation of nitrogenase activity in Rhodospirillum rubrum. This report describes the physiological effects of mutations in the genes encoding the enzymes that add and remove the ADP-ribosyl moiety. Mutants lacking a functional draT gene had no dinitrogenase reductase ADP-ribosyltransferase (DRAT, the draT gene product) activity in vitro and were incapable of modifying dinitrogenase reductase with ADP-ribose in vivo. Mutants lacking a functional draG gene had no dinitrogenase reductase-activating glycohydrolase (DRAG, the draG gene product) activity in vitro and were unable to remove ADP-ribose from the modified dinitrogenase reductase in vivo. Strains containing polar mutations in draT had no detectable DRAG activity in vitro, suggesting likely cotranscription of draT and draG. In strains containing draT and lacking a functional draG, dinitrogenase reductase accumulated in the active form under derepressing conditions but was rapidly ADP-ribosylated in response to conditions that cause inactivation. Detection of DRAT in these cells in vitro demonstrated that DRAT is itself subject to posttranslational regulation in vivo. Mutants affected in an open reading frame immediately downstream of draTG showed regulation of dinitrogenase reductase by ADP-ribosylation, although differences in the rates of ADP-ribosylation were apparent.Rhodospirillum rubrum, a purple, nonsulfur, photosynthetic bacterium, has a well-characterized system of posttranslational regulation of its nitrogenase by ADP-ribosylation. The nitrogenase complex consists of two proteins: dinitrogenase, an a232 tetramer of the nifK and nifD gene products, contains the active site of nitrogenase, and dinitrogenase reductase, an a2 dimer of the nifH gene product, supplies the reducing power to dinitrogenase. Regulation of the complex is achieved by reversible mono-ADP-ribosylation of dinitrogenase reductase at Arg-101 (23) in response to light level and a fixed nitrogen concentration (12).Two enzymes have been shown to perform this regulation in vitro. Dinitrogenase reductase ADP-ribosyltransferase (DRAT, the gene product of dra7) transfers an ADP-ribose from NAD to one subunit of dinitrogenase reductase (18,20), thereby inactivating nitrogenase by preventing electron flow within the nitrogenase complex (22). Dinitrogenase reductase-activating glycohydrolase (DRAG, the gene product of draG) removes the ADP-ribosyl group from dinitrogenase reductase, restoring activity to the nitrogenase complex (21, 28-30). The draT and draG genes have been isolated and sequenced (7) and are adjacent to, but transcribed in the opposite direction from, the nifHDK genes (15).The first description of mono-ADP-ribosylation was that of eucaryotic elongation factor 2 by diphtheria toxin (11). Subsequently, a number of other bacterial toxins, including cholera toxin and pertussis toxin, have been shown to act by ADP-ribosylating proteins in eucaryotic cells (reviewed in * Corresponding aut...

In Anabaena 7120, heterocysts (cells specialized for nitrogen fixation) develop at the ends of filaments and at intervals within each fiament. We have isolated a mutant Anabaena strain that develops heterocysts mostly at the ends of filaments. This mutant, PAT-1, grows poorly under nitrogenfixing conditions. The wild-type gene that complements the mutation in PAT-1, calledpaL4, was cloned and sequenced. The

Kraft lignin (KL), the byproduct from the alkali pulping process in the paper industry, is an abundant renewable resource. It was found that KL could be used to form nanocapsules via self-assembly induced by adding water to an ethanol solution of KL. From the results of various imaging techniques and laser light scattering techniques, the hollow sphere feature of this product was confirmed. It was found that there is a higher percentage of ethanol enriched in the interior of the nanocapsules and that the different KL fractions can be spontaneously distributed in the shells according to their hydrophilic–lipophilic sequence. The π–π interactions between the aromatic rings are considered to be an important driving force in the assembly process of the KL nanocapsules. Moreover, the sizes of these KL nanocapsules can vary in the range of tens to hundreds of nanometers, depending on the preparation conditions, which enhance their flexibility to adapt to the potential applications in various fields. Preparation of KL nanocapsules requires only a simple mix of KL/ethanol solution and water, which is a totally green process utilizing a renewable resource.

A mutant of Anabaena sp. strain PCC 7120, called PAT-2, that grows poorly under nitrogen-fixing conditions, has been isolated. The heterocysts of the mutant strain develop much more slowly than those of the wild type and are spaced more closely in an older culture of the mutant than in the wild type. The wild-type gene that complements the mutation in PAT-2, called patB, was isolated and characterized. The predicted 529-amino-acid PatB protein contains a region very similar to the Fe4S4 bacterial-type ferredoxins near its N terminus and a helix-turn-helix motif near its C terminus. This pattern of domains resembles those of transcriptional regulators in both prokaryotes and eukaryotes. The mutation in strain PAT-2 is the deletion of G at nucleotide 1342 in the patB gene, resulting in the loss of a 62-amino-acid fragment from the C terminus of the PatB protein, including the helix-turn-helix motif.