Nif regulon

The Nif regulon is a set of seven operons used to regulate nitrogen fixation in the coliform bacterium Klebsiella pneumoniae under anaerobic and microaerophilic conditions.

The nif regulon comprises 7 operons: nifRLA, nifJ, nifHDK, nifEN, nifUSVM, nifWF, nifBQ.

nifEN and nifBQ operons: This comprises nifE, nifN, nifB and nifQ genes which are responsible for formation of a functional Mo-Fe protein.

nifUSVM operon: The nifS, nifV and nifM genes encode for a protein that is required to process component II.

[3] The Nif regulon is regulated in response to a variety of environmental signals to ensure nitrogen-fixation only occurs when necessary: The action site of O2 is the nifL protein which is basically a flavoprotein with FAD as the redox sensing cofactor.

Fnr (fumarate nitrate reduction regulator) is the signal transduction molecule which transduces the oxygen status to the nifL protein.

This modified enzyme binds to the nifR region of the nifRLA operon and prevents the transcription of the genes, nifL and nifA.