RESUMO
Pathogenic isolates of Periconia circinata produce a host-specific toxin (PC-toxin) and cause a root and crown rot in susceptible genotypes of sorghum. Treatment with PC-toxin leads to selective development of disease symptoms and an increase in synthesis of a group of acidic, low molecular weight proteins only in susceptible genotypes. Treatment of sorghum seedlings or excised root tips with HgCl(2) resulted in responses indistinguishable from those produced by treatment with PC-toxin, but the effects were not genotype specific.
RESUMO
We isolated 142 Hir- (host inhibition of replication) mutants of an Escherichia coli K-12 Mu cts Kil- lysogen that survived heat induction and the killing effect of Mu replicative transposition. All the 86 mutations induced by insertion of Tn5 or a kanamycin-resistant derivative of Tn10 and approximately one-third of the spontaneous mutations were found by P1 transduction to be linked to either zdh-201::Tn10 or Tn10-1230, indicating their location in or near himA or hip, respectively. For a representative group of these mutations, complementation by a plasmid carrying the himA+ gene or by a lambda hip+ transducing phage confirmed their identification as himA or hip mutations, respectively. Some of the remaining spontaneously occurring mutations were located in gyrA or gyrB, the genes encoding DNA gyrase. Mutations in gyrA were identified by P1 linkage to zei::Tn10 and a Nalr gyrA allele; those in gyrB were defined by linkage to tna::Tn10 and to a gyrB(Ts) allele. In strains carrying these gyrA or gyrB mutations, pBR322 plasmid DNA exhibited altered levels of supercoiling. The extent of growth of Mu cts differed in the various gyrase mutants tested. Phage production in one gyrA mutant was severely reduced, but it was only delayed and slightly reduced in other gyrA and gyrB mutants. In contrast, growth of a Kil- Mu was greatly reduced in all gyrase mutant hosts tested.
Assuntos
Bacteriófago mu/fisiologia , Elementos de DNA Transponíveis , Escherichia coli/genética , Proteínas de Bactérias/genética , Proteínas de Bactérias/fisiologia , Bacteriófago mu/genética , DNA Topoisomerases Tipo II/genética , DNA Topoisomerases Tipo II/fisiologia , DNA Viral/genética , Escherichia coli/fisiologia , Fatores Hospedeiros de Integração , Lisogenia , Replicação ViralRESUMO
The objective of these studies is to define the role of zinc in RBC ghost morphology specifically in comparison to the echinocytogenic effects of calcium. Erythrocyte ghosts were prepared from patients with sickle cell anemia, treated with zinc and/or calcium and the resulting cell morphology studied by scanning electron microscopy. Our results showed that zinc consistently and significantly antagonized the echinocytogenic effect of calcium. A simple log linear statistical model was used to evaluate the data and supported this conclusion. We discuss the potential significance of these findings to the effect of zinc treatment on patients with sickle cell anemia.
