Conserved Nodulation Genes in Rhizobium meliloti and Rhizobium trifolii

Plasmids which contained wild-type or mutated Rhizobium meliloti nodulation (nod) genes were introduced into Nod⁻R. trifolii mutants ANU453 and ANU851 and tested for their ability to nodulate clover. Cloned wild-type and mutated R. meliloti nod gene segments restored ANU851 to Nod⁺, with the exception of nodD mutants. Similarly, wild-type and mutant R. meliloti nod genes complemented ANU453 to Nod⁺, except for nodCII mutants. Thus, ANU851 identifies the equivalent of the R. meliloti nodD genes, and ANU453 specifies the equivalent of the R. meliloti nodCII genes. In addition, cloned wild-type R. trifolii nod genes were introduced into seven R. meliloti Nod⁻ mutants. All seven mutants were restored to Nod⁺ on alfalfa. Our results indicate that these genes represent common nodulation functions and argue for an allelic relationship between nod genes in R. meliloti and R. trifolii.     

Rhizobium meliloti nodulation genes: identification of nodDABC gene products, purification of nodA protein, and expression of nodA in Rhizobium meliloti.

A set of conserved, or common, bacterial nodulation (nod) loci is required for host plant infection by Rhizobium meliloti and other Rhizobium species. Four such genes, nodDABC, have been indicated in R. meliloti 1021 by genetic analysis and DNA sequencing. An essential step toward understanding the function of these genes is to characterize their protein products. We used in vitro and maxicell Escherichia coli expression systems, together with gel electrophoresis and autoradiography, to detect proteins encoded by nodDABC. We facilitated expression of genes on these DNA fragments by inserting them downstream of the Salmonella typhimurium trp promoter, both in colE1 and incP plasmid-based vectors. Use of the incP trp promoter plasmid allowed overexpression of a nodABC gene fragment in R. meliloti. We found that nodA encodes a protein of 21 kilodaltons (kDa), and nodB encodes one of 28 kDa; the nodC product appears as two polypeptide bands at 44 and 45 kDa. Expression of the divergently read nodD yields a single polypeptide of 33 kDa. Whether these represent true Rhizobium gene products must be demonstrated by correlating these proteins with genetically defined Rhizobium loci. We purified the 21-kDa putative nodA protein product by gel electrophoresis, selective precipitation, and ion-exchange chromatography and generated antiserum to the purified gene product. This permitted the immunological demonstration that the 21-kDa protein is present in wild-type cells and in nodB- or nodC-defective strains, but is absent from nodA::Tn5 mutants, which confirms that the product expressed in E. coli is identical to that produced by R. meliloti nodA. Using antisera detection, we found that the level of nodA protein is increased by exposure of R. meliloti cells to plant exudate, indicating regulation of the bacterial nod genes by the plant host.     

Effects of histamine on bronchial artery blood flow and bronchomotor tone

The effects of aerosolized 5% histamine (10 breaths) on bronchial artery blood flow (Qbr), airflow resistance (RL), and pulmonary and systemic hemodynamics were studied in mechanically ventilated sheep anesthetized with pentobarbital sodium. Histamine increased mean Qbr and RL to 252 +/- 45 and 337 +/- 53% of base line, respectively. This effect was significantly different from base line for 30 min after challenge. The histamine-induced increase in RL was blocked by pretreatment with the histamine H1 receptor antagonist, chlorpheniramine, whereas the histamine-induced elevation in Qbr was prevented by the H2 antagonist, metiamide. Both responses were blocked only when both antagonists were present. Changes in Qbr were not directly associated with alterations in systemic and pulmonary hemodynamics or arterial blood gas composition. In vitro histamine caused a dose-dependent contraction of ovine bronchial artery strips that was prevented by H1 antagonist. The H2 agonist, impromidine, caused relaxation of precontracted arterial strips and was more potent and efficacious than histamine, whereas H1 agonists failed to elicit a relaxant response. Thus these findings indicate that histamine aerosol induces a vasodilation in the bronchial vascular bed; histamine has a direct effect on Qbr that is independent of alterations in RL, systemic and pulmonary hemodynamics, or arterial blood gas composition; and, histamine-induced bronchoconstriction is mediated predominantly by H1-receptors, whereas increased Qbr is controlled predominantly by H2-receptors, probably located in resistance vessels. This local effect of histamine on Qbr may have important implications in the pathophysiology of bronchial asthma and pulmonary edema.     

Generalized transduction in Rhizobium meliloti.

Generalized transduction of Rhizobium meliloti 1021 was carried out by bacteriophage N3. Genetic markers on the chromosome and the pSym megaplasmid were transduced, along with markers on several IncP plasmids. Cotransduction between transposon Tn5 insertions and integrated recombinant plasmid markers permitted correlation of cotransductional frequencies and known physical distances. Bacteriophage N3 was capable of infecting several commonly used strains of R. meliloti.     

Inhibition of the DNA catenation activity of type II topoisomerase by VP16-213 and VM26

Studies suggest that the anticancer drugs VP16-213 and VM26 produce cytotoxicity by inducing protein-associated DNA breakage in vivo through interaction with a yet unknown nuclear component. The effects of these drugs and their congeners on topoisomerase activities was investigated. VP16-213, VM26, and congeners active toward inducing DNA breaks also inhibited the catenation activity of eukaryote type II topoisomerase in vitro at very low drug concentrations. A structure-activity relationship was obtained for inhibition of catenation that parallels in vivo DNA breakage and cytotoxic activities. Type I topoisomerase activity was totally unaffected by these drugs.     

Localization and synthesis of an antigenic determinant of herpes simplex virus glycoprotein D that stimulates the production of neutralizing antibody.

An antigenic determinant capable of inducing type-common herpes simplex virus (HSV)-neutralizing antibodies has been located on glycoprotein D (gD) of HSV type 1 (HSV-1). A peptide of 16 amino acids corresponding to residues 8 to 23 of the mature glycoprotein (residues 33 to 48 of the predicted gD-1 sequence) was synthesized. This peptide reacted with an anti-gD monoclonal antibody (group VII) previously shown to neutralize the infectivity of HSV-1 and HSV-2. The peptide was also recognized by polyclonal antibodies prepared against purified gD-1 but was less reactive with anti-gD-2 sera. Sera from animals immunized with the synthetic peptide reacted with native gD and neutralized both HSV-1 and HSV-2.     

Control of chicken coccidiosis

Coccidiosis could potentially cause enormous economic loss to the poultry industry, especially in the production of broiler chickens (see Box 1). Losses are currently minimized by chemotherapeutic treatment but the effectiveness of many drugs seems to be declining. In this article, Peter Long and Tom Jeffers discuss the future for coccidial chemotherapy, and the potential for immunological control methods.     

Brain temperature measurements in rats: a comparison of microwave and ambient temperature exposures

In an effort to understand microwave heating better, regional brain and core temperatures of rats exposed to microwave radiation (2450 MHz) or elevated air temperatures were measured in two studies. In general, we have found no substantial evidence for temperature differentials, or "hot spots," in the brain of these animals. In the first study, after a 30-min exposure, no temperature differences between brain regions either after microwave or ambient air exposure were found. However, a highly significant correlation between brain and core temperatures was found and this correlation was the same for both microwave and ambient air heating. In the second study, time-temperature profiles were measured in rats exposed to either 30 mW/cm2 or 36.2 degrees C. In this study, the 30-min exposure period was divided into seven intervals and the change in temperature during each period was analyzed. Only the cortex showed significantly different heating rates between the air heating and microwave heating; however, this difference disappeared after the initial 5 min of exposure.