| Autor: |
Lei, Shi, Pulakat, Lakshmidevi, Gavini, Narasaiah |
| Zdroj: |
Biochemical and Biophysical Research Communications; October 1999, Vol. 264 Issue: 1 p186-190, 5p |
| Abstrakt: |
Azotobacteris a diazotrophic bacterium that harbors three genetically distinct nitrogenases referred to as nif, vnf,and anfsystems. The nifMis an accessory gene located in the nifgene cluster and is transcriptionally regulated by the NifA. However, Azotobactermutants that lack NifA are known to synthesize functional NifM and this accessory protein is known to be needed for the activity of nitrogenase-2 and nitrogenase-3. To determine how the transcription of nifMis regulated when Azotobacteris grown under conditions in which nitrogenase-2 or nitrogenase-3 is expressed, we generated an Azotobacter vinelandiistrain that carries a nifM:lacZ-kanamycin resistance gene cassette in its chromosome. In this strain the nifMopen reading frame was disrupted by the presence of a lacZ-kanamycin resistance gene cassette so that it could not produce active NifM. Moreover, the lacZgene was placed under the transcriptional control elements of the nifMgene so that the lacZexpression could be used as a marker to determine the extent of expression of the nifMgene under different growth conditions. Our results show that this strain was unable to grow in Burk's nitrogen-free medium supplemented with either molybdenum or vanadium or lacking both metals suggesting that in the absence of functional NifM none of the nitrogenases were active. It was also found that the nifMexpression was differentially regulated when the A. vinelandiicells were grown under conditions that activate nitrogenase-2 and nitrogenase-3, as determined by liquid β-galactosidase activity measurements. These results suggest that the transcriptional activators, VnfA and AnfA, may regulate the nifMexpression. |
| Databáze: |
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