Results and Discussion

Increasing concentrations of the N-terminal domain inhibited DNA-binding (Figure 1) and ATPase activity (Figure 2) of the N-truncated NifA protein. The N-terminal domain also inhibited proteolysis of the N-truncated NifA. These results indicated a direct contact of the N-terminal domain with the Central and/or C-terminal domains of the N-truncated NifA, and support. These results confirm the observation that the N-terminal domain negatively controls NifA activity in vivo (Monteiro et al. 1999b). The N-terminal domain of H. seropedicae NifA also strongly inhibited ATP hydrolysis by Azotobacter vinelandii NifA but not by the K. pneumoniae NtrC, indicating the specific nature of the binding to the NifA protein.

<-DNA-protein

<-DNA-protein

Figure 1. Inhibition of DNA-binding activity by the N-terminal domain.

N-terminal/AN-NifA (molar ratio) 0 1 2 5 10

ADP ATP

Figure 1. Inhibition of DNA-binding activity by the N-terminal domain.

N-terminal/AN-NifA (molar ratio) 0 1 2 5 10

ADP ATP

Figure 2. Inhibition of ATPase activity by the N-terminal domain.

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