CYS-184 AND CYS-187 OF NIFL PROTEIN OF KLEBSIELLA-PNEUMONIAE ARE NOT ABSOLUTELY REQUIRED FOR INHIBITION OF NIFA ACTIVITY

The sequence Cys184-Ala-Asp-Cys187 in the NifL protein of Klebsiella pneumoniae, for which a role in oxygen sensing and/or metal binding has been proposed, was altered by introducing two mutations, Cys184 --> Ala and Cys187 --> Ala, using oligodeoxyribonucleotide-directed mutagenesis. Neither mutation abolished ammonium or oxygen control of nif transcription, although some impairment of function was apparent. The two Cys residues are therefore unlikely to have a direct role in oxygen sensing or metal binding, but probably make some contribution to protein folding or stability.