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Vol. 171, No. 6 The Central Domain of Rhizobium meliloti NifA Is Sufficient To

Summary: Vol. 171, No. 6
The Central Domain of Rhizobium meliloti NifA Is Sufficient To
Activate Transcription from the R. meliloti nifH Promoter
Department of Genetics, Harvard Medical School, and Department of Molecular Biology,
Massachusetts General Hospital, Boston, Massachusetts 02114
Received 23 January 1989/Accepted 22 March 1989
The Rhizobium meliloti nifA product (NifA) shares extensive homology in its central region and at its
C-terminal end with Rhizobium leguminosarum DctD and with NtrC from several species. All three proteins are
transcriptional activators of NtrA (RpoN)-RNA polymerase-dependent promoters. Several large deletions ofR.
meliloti NifA were constructed to investigate the role of the conserved and divergent domains of NifA in
transcriptional activity and posttranscriptional regulation by oxygen. The ability of NifA expressed from the
Escherichia coli lacZ promoter to activate the R. meliloti nip promoter in E. coli and R. meliloti was tested
under a range of defined atmospheric oxygen partial pressures. Deletion of the divergent N-terminal domain
of NifA had little effect on NifA activity and no effect on oxygen sensitivity. Deletion of the conserved C-terminal
helix-turn-helix motifof NifA did not eliminate NifA-dependent activation of the nifH promoter, although it did
decrease NifA activity about twofold in E. coil and 10-fold in R. meliloti. A NifA carrying both the N-terminal
and C-terminal deletions and consisting of only the central highly conserved domain and 50 divergent amino
acids retained the ability to activate transcription from the niJU promoter. The transcriptional activity of the
conserved central domain is consistent with the prediction that the core domain is the part of NifA which


Source: Ausubel, Frederick M. - Department of Genetics, Harvard University


Collections: Biology and Medicine