Nif Gene Products and Their Roles in Nitrogen Fixation

Abstract

More advances in our understanding of the roles of the various nif-specific gene products in biological nitrogen fixation have occurred in the 2+ years since the Knoxville meeting than in any period following the original designation of gene product relationships by Roberts et al. (1978). Several nif gene products have been isolated, the biochemical properties of some have been determined and the roles of a number of the products have been established or proposed. Table 1 lists the known nif genes from K. pneumoniae and provides a brief description of the roles that each have been shown or proposed to play in the nitrogenase catalysis or the assembly of those gene products involved in catalysis. Information regarding the role of nif gene products in assembly, maturation or stability of the nitrogenase complex has come primarily from the Azotobacter vinelandii and Kiebsiella pneumoniae systems, but homologs for genes encoding the proteins assigned to various functions have been found in several organisms. As the structural information regarding the nitrogenase proteins becomes more definitive, our attention will turn to how those structural entities are assembled, how they function and how they are maintained in the cell.