Molecular Analysis of the glnB, amtB, glnD and glnA Genes in Azotobacter Vinelandii

Abstract

Several genes in Azotobacter vinelandii have products involved in regulating responses to fixed N levels; these include nifLA, ntrBC, glnB, and glnD (nfrX). In cells with sufficient fixed N, NifL antagonizes NifA, the transcriptional activator of expression of other nif genes. Because glnD::Tn5 mutants are Nif⁻ and suppressed to Nif⁺ by a nifL:KIXX mutation (Contreras et al. 1991), a working model is that GlnD is required for conversion of active NifL (inhibitory to NifA) to an inactive form. In enteric and other bacteria, GlnD uridylylates the PII protein under conditions of low N and removes UMP from PII-UMP when fixed N is plentiful. Our aims were to determine whether the glnB-encoded PII protein influences NifL activity and to characterize the role of GlnD in nitrogen fixation.