Nifa Protein Function And Multiple Copies Of Nifa Gene Promotion, Nitrogen Fixation Efficacy Of S. Meliloti (sinorhizobium Meliloti,)

Replacement of the conserved amino acid residue Thr-290 by Val in the C3 central domain region of Klebsiella pneumoniae (Kp) NifA resulted in a loss of transcriptional activation of nif genes. Thus, the conserved Thr-290 residue appears to be critical for functional activation of the NifA central domain. We used this point mutant in a merodiploid experiment to examine the putative multimerization function of the NifA central domain. The result of this experiment showed that this domain contained the multimerizartion determinants of the NifA protein. A series of truncation mutants of NifA was constructed to determine those structural elements within the central domain that are critical for multimerization. Our data demonstrate that amino acid residues 252-453 are involved in the multimerization process.