Cloning, sequencing, mutagenesis, and functional characterization of draT and draG genes from Azospirillum brasilense.

AUTOR(ES)

Zhang, Y

RESUMO

The Azospirillum brasilense draT gene, encoding dinitrogenase reductase ATP-ribosyltransferase, and draG gene, encoding dinitrogenase reductase activating glycohydrolase, were cloned and sequenced. Two genes were contiguous on the A. brasilense chromosome and showed extensive similarity to the same genes from Rhodospirillum rubrum. Analysis of mutations introduced into the dra region on the A. brasilense chromosome showed that mutants affected in draT were incapable of regulating nitrogenase activity in response to ammonium. In contrast, a mutant with an insertion in draG was still capable of ADP-ribosylating dinitrogenase reductase in response to ammonium but was no longer able to recover activity after ammonium depletion. Plasmid-borne draTG genes from A. brasilense were introduced into dra mutants of R. rubrum and restored these mutants to an apparently wild-type phenotype. It is particularly interesting that dra mutants of R. rubrum containing draTG of A. brasilense can respond to darkness and light, since A. brasilense is a nonphotosynthetic bacterium and its dra system does not normally possess that regulatory response. The nifH gene of A. brasilense, encoding dinitrogenase reductase (the substrate of dinitrogenase reductase ADP-ribosyltransferase and dinitrogenase reductase-activating glycohydrolase), is located 1.9 kb from the start of draT and is divergently transcribed. Two insertion mutations in the region between draT and nifH showed no significant effect on nitrogenase activity or its regulation.

Documentos Relacionados

• Mutations in the draT and draG genes of Rhodospirillum rubrum result in loss of regulation of nitrogenase by reversible ADP-ribosylation.
• Cloning, nucleotide sequencing, and expression of the Azospirillum brasilense lon gene: involvement in iron uptake.
• Purification and characterization of glutamate synthase from Azospirillum brasilense.
• Cloning, sequencing, and phenotypic analysis of laf1, encoding the flagellin of the lateral flagella of Azospirillum brasilense Sp7.
• Cloning, sequencing, expression and characterization of DNA photolyase from Salmonella typhimurium.