Regulation of reduced nitrogen assimilation in Rhodobacter capsulatus E1F1

The phototrophic bacterium Rhodobacter capsulatus E1F1 assimilates ammonia and other forms of reduced nitrogen either through the GS/GOGAT pathway or by the concerted action of l-alanine dehydrogenase and aminotransferases. These routes are light-independent and very responsive to the carbon and nitrogen sources used for cell growth. GS was most active in cells grown on nitrate or l-glutamate as nitrogen sources, whereas it was heavily adenylylated and siginificantly repressed by ammonium, glycine, l-alanine, l-aspartate, l-asparagine and l-glutamine, under which conditions specific aminotransferases were induced. GOGAT activity was kept at constitutive levels in cells grown on l-amino acids as nitrogen sources except on l-glutamine where it was significantly induced during the early phase of growth. In vitro, GOGAT activity was strongly inhibited by l-tyrosine and NADPH. In cells using l-asparagine or l-aspartate as nitrogen source, a concerted induction of l-aspartate aminotransferase and l-asparaginase was observed. Enzyme level enhancements in response to nitrogen source variation involved de novo protein synthesis and strongly correlated with the cell growth phase.Abbreviations ADH l-alanine dehydrogenase - AOAT l-alanine:2-oxoglutarate aminotransferase - Asnase l-asparaginase - GOAT Glycine: oxaloacetate aminotransferase - GOGAT Glutamate synthase - GOT l-aspartate: 2-oxoglutarate aminotransferase - GS Glutamine synthetase - HPLC High-Pressure Liquid Chromatography - MOPS 2-(N-morpholino)propanesulfonic acid - MSX l-methionine-d,l-sulfoximine     

Multimeric arrays of the yeast retrotransposon Ty.

We have identified a novel integrated form of the yeast retrotransposon Ty consisting of multiple elements joined into large arrays. These arrays were first identified among Ty-induced alpha-pheromone-resistant mutants of MATa cells of Saccharomyces cerevisiae which contain Ty insertions at HML alpha that result in the expression of that normally silent cassette. These insertions are multimeric arrays of both the induced genetically marked Ty element and unmarked Ty elements. Structural analysis of the mutations indicated that the arrays include tandem direct repeats of Ty elements separated by only a single long terminal repeat. The Ty-HML junction fragments of one mutant were cloned and shown to contain a 5-base-pair duplication of the target sequence that is characteristic of a Ty transpositional insertion. In addition, the arrays include rearranged Ty elements that do not have normal long terminal repeat junctions. We have also identified multimeric Ty insertions at other chromosomal sites and as insertions that allow expression of a promoterless his3 gene on a plasmid. The results suggest that Ty transposition includes an intermediate that can undergo recombination to produce multimers.     

Tandem duplications of the lac region of the Escherichia coli chromosome

Tandem duplications are caused by unequal crossing over between homologous sequences. Duplications in the lac region of the Escherichia coli chromosome were isolated by two methods. Duplication frequency using a method involving P1 transduction increased from 0.4% with no UV to 2.0% following UV irradiation at 35 J/m2. Duplication frequency in lac using a second generalizable method that does not involve P1 transduction increased from 0.7 to 12% at 35 J/m2 UV. In both cases the duplication frequency began to plateau at UV doses of 12 J/m2 and 24 J/m2. According to segregation analysis of sixteen duplications there may be at least seven classes of duplications isolated by each method. Pulsed-field gel electrophoresis was used to measure the duplications isolated without P1 transduction. The minimum size of the duplications ranged from 30 to 320 kb but could be much larger.     

Branch capture reactions: displacers derived from asymmetric PCR.

Branch capture reactions (BCR) contain three DNA species: (i) a recipient restriction fragment terminating in an overhang, (ii) a displacer strand containing two adjacent sequences, with one complementary to the overhang and to contiguous nucleotides within the recipient duplex and (iii) a linker which is complementary to the second displacer sequence. Branched complexes containing all three species may be captured by ligation of the linker to the recipient overhang. The use of 5-MedC in the displacer facilitates BCR. High temperature ligation with a thermostable enzyme increased specificity for ligation to the correct recipient in a complex mixture of restriction fragments. Displacer synthesis by PCR permitted separate reactions of formation of stable displacement complexes and of high-temperature ligation. Ethylene glycol-containing buffer permitted PCR with 5-MedCTP or high G + C products using thermostable polymerases. BCR may be used to modify the ends of one recipient DNA duplex in a population of duplex DNA fragments. Modification of the recipient could be used to facilitate detection, affinity chromatography or cloning. By using PCR to obtain a BCR displacer, the sequence non-homologous to the recipient duplex may be expanded to include the sequence of a selectable marker, thus facilitating chromosome walking.     

Effects of granuloma modulation induced by regulatory-T-lymphocyte activity on angiotensin II/III production by granuloma macrophages in murine schistosomiasis mansoni

Angiotensins are produced by granuloma macrophages in murine Schistosoma mansoni. During the course of infection, granuloma undergo a T-cell-dependent process called modulation in which their maximal size decreases. This study was undertaken to establish whether angiotensin production by granuloma macrophages is altered by immunoregulatory lymphocytes. Granuloma macrophages from modulated lesions released and contained more angiotensin II/III (AII/III) and less angiotensin I (AI) than those from the acute infection. Captopril, a specific angiotensin-converting-enzyme (ACE) inhibitor, appreciably decreased AII/III produced by macrophages from modulated granulomas. Adoptive transfer of splenic T lymphocytes from chronically infected donors into acutely infected recipients altered angiotensin production by the granuloma macrophages in a manner similar to that seen in modulated lesions. However, no difference was detected in the capacity of granuloma macrophages from acutely or chronically infected mice to metabolize 125I-AI or -AII added to cell cultures. Similarly, captopril did not alter the metabolism of exogenously administrated angiotensins. These findings suggest that regulatory T lymphocytes influence the metabolism by granuloma macrophages of endogenously produced angiotensins at least in part by induction of macrophage ACE activity. However, the degradation of extracellular AI and AII may result from the activity of enzymes other than ACE which are not inducible by modulation.     

Induction of granuloma modulation in murine schistosomiasis mansoni by enteric exposure to schistosome eggs

Enteric administration of antigen can induce systemic tolerance. In murine schistosomiasis mansoni, blood flukes produce eggs which enter the intestine. An immunologic phenomenon associated with this disease is a spontaneous diminution in the intensity of the granulomatous response in the liver, lungs, and colonic mucosa with chronic infection, which is termed modulation. It was determined whether modulation of liver granulomas could be induced by enteric immunization with schistosome eggs. Mice infected for 4 wk were immunized by injection of 25,000 eggs into cecal pouches. This induced modulation of liver granulomas by the eighth week of infection. Neither cecal injection of normal saline nor i.p. or subcutaneous injection of eggs could induce the modulatory process. Modulation could be adoptively transferred from enterically immunized donors by injection of spleen cells into infected recipients or into uninfected recipients with synchronous liver granulomas induced by the hepatic embolization of schistosome eggs. Spleen cells treated with anti-Thy-1.2 or anti-Lyt-1.1 and complement could no longer adoptively transfer modulation. These data show that enteric immunization with schistosome eggs can induce modulation of the liver granuloma by a cellular mechanism similar to that described for the natural infection.     

Transposable lambda placMu bacteriophages for creating lacZ operon fusions and kanamycin resistance insertions in Escherichia coli.

We have constructed several derivatives of bacteriophage lambda that translocate by using the transposition machinery of phage Mu (lambda placMu phages). Each phage carries the c end of Mu, containing the Mu cIts62, ner (cII), and A genes, and the terminal sequences from the Mu S end (beta end). These sequences contain the Mu attachment sites, and their orientation allows the lambda genome to be inserted into other chromosomes, resulting in a lambda prophage flanked by the Mu c and S sequences. These phages provide a means to isolate cells containing fusions of the lac operon to other genes in vivo in a single step. In lambda placMu50, the lacZ and lacY genes, lacking a promoter, were located adjacent to the Mu S sequence. Insertion of lambda placMu50 into a gene in the proper orientation created an operon fusion in which lacZ and lacY were expressed from the promoter of the target gene. We also introduced a gene, kan, which confers kanamycin resistance, into lambda placMu50 and lambda placMu1, an analogous phage for constructing lacZ protein fusions (Bremer et al., J. Bacteriol. 158:1084-1093, 1984). The kan gene, located between the cIII and ssb genes of lambda, permitted cells containing insertions of these phages to be selected independently of their Lac phenotype.     

Measurement of in vivo expression of the recA gene of Escherichia coli by using lacZ gene fusions.

A recA-lacZ protein fusion was constructed in vivo by using bacteriophage Mu dII301(Ap lac). The fusion contained the promoter and first 47 codons of the recA mutant, as determined by DNA sequence analysis. The fusion was cloned and used to construct a recA-lacZ operon fusion at the same site within the recA gene. These fusions were introduced into the Escherichia coli chromosome at the lambda attachment site either as complete or cryptic lambda prophages. Synthesis of beta-galactosidase from these fusions was inducible by UV radiation. As the UV dose was increased, induction became slower and persisted for a longer period of time. At low doses of UV radiation, more beta-galactosidase was produced in a uvrA mutant than in a wild-type strain; however, at high doses, no induced synthesis of beta-galactosidase occurred in a uvrA mutant. recA+ strains carrying either the protein or operon fusion on a multicopy plasmid showed reduced survival after UV irradiation. This UV sensitivity was not exhibited by strains containing a single copy of either fusion, however; hence, the fusions provide a reliable measure of recA expression.