CONSERVATION BETWEEN RHIZOBIUM NIF, NTR AND DCT GENES

Project: Research project

Project Details

Description

Recent studies are consistent with a two-component model of
sensory transduction and transcriptional regulation that applies to
a number of biological responses in many eubacterial species.
Functional domains appear to have evolved to make repeated use
of existing protein-protein and protein-DNA interactions to
create novel regulatory systems. Validating the presence of these
functional domains can be achieved by either following regulatory
phenotypes after rearranging existing domains in hybrid genes of
by mapping second site reversions of numerous point mutations to
demonstrate interactive domains. Experiments are designed to
utilize C4-dicarboxylate transport (dct), nitrogen fixation (nif)
and nitrogen assimilation (ntr) genes of Rhizobium to test the
validity of the model; results will simultaneously reveal
mechanisms of gene expression essential to biological nitrogen
fixation. Previous work provides nif structural genes and
appropriate promoter::reporter gene constructions, regulatory
genes nifA, ntrB and ntrC, and the alternate sigma factor encoded
by ntrA. Unpublished work provides the dctA structural gene and
regulatory genes dctB and dctD. Hybrid genes, expression vectors
for producing regulatory proteins, a dctA::lacZ fusion gene for
reporting transcription and various mutant strains will be
constructed. These tools will then facilitate phenotype screening
to discover how similar polypeptide regions are used in a specific
fashion to regulate numerous pathways in Rhizobium meliloti.
Broad academic and practical interest in this study is anticipated
because related gene products control plant tumor formation by
Agrobacteria, sporulation by Bacillus and phosphate scavenging
and chemotaxis in enterics; similar genes are also implicated in
initiation and maintenance of infection by several gram negative
pathogens by controlling expression of pillin genes, regulation of
differentiation by Caulobacter, and control of expression of
xylose degredation genes and carboxypeptidase G2 in
Pseudomonas.
StatusFinished
Effective start/end date7/1/884/30/92

Funding

  • National Institutes of Health
  • National Institutes of Health
  • National Institutes of Health

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