ISSN:
1432-072X
Keywords:
Bradyrhizobium japonicum
;
NifA activity
;
nifA mRNA half-lives
;
Oxygen shift
;
Post-transcriptional control
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract Previous work had shown that Bradyrhizobium japonicum nifA-dependent nif gene activation was inhibited by oxygen via a post-transcriptional mechanism. In the present report we demonstrate that this inhibition occurs at the NifA protein level and that it is irreversible. To narrow down the level of control the influence of oxygen on nifA mRNA stability and NifA protein activity was analyzed. The half-lives of B. japonicum and Klebsiella pneumoniae (control) nifA mRNAs derived from constitutively expressed nifA genes did not differ significantly under aerobic and anaerobic conditions which makes it unlikely that oxygen exerts its effect by selectively destabilizing B. japonicum nifA mRNA. By making use of its ability to activate in Escherichia coli a B. japonicum nifD' — 'lacZ fusion, the NifA protein was assayed by the determination of lacZ mRNA and β-galactosidase synthesis. Oxygen shift experiments clearly demonstrated that B. japonicum NifA activity (but not that of K. pneumoniae) was drastically reduced within minutes upon a shift to aerobiosis and that the inactivation was irreversible.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00413129
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