Effect of P II and Its Homolog GlnK on Reversible ADP-Ribosylation of Dinitrogenase Reductase by Heterologous Expression of the Rhodospirillum rubrum Dinitrogenase Reductase ADP-Ribosyl Transferase–Dinitrogenase Reductase-Activating Glycohydrolase Regulatory System in Klebsiella pneumoniae

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Abstract
Reversible ADP-ribosylation of dinitrogenase reductase, catalyzed by the dinitrogenase reductase ADP-ribosyl transferase–dinitrogenase reductase-activating glycohydrolase (DRAT-DRAG) regulatory system, has been characterized in Rhodospirillum rubrum and other nitrogen-fixing bacteria. To investigate the mechanisms for the regulation of DRAT and DRAG activities, we studied the heterologous expression of R. rubrum draTG in Klebsiella pneumoniae glnB and glnK mutants. In K. pneumoniae wild type, the regulation of both DRAT and DRAG activity appears to be comparable to that seen in R. rubrum . However, the regulation of both DRAT and DRAG activities is altered in a glnB background. Some DRAT escapes regulation and becomes active under N-limiting conditions. The regulation of DRAG activity is also altered in a glnB mutant, with DRAG being inactivated more slowly in response to NH 4 + treatment than is seen in wild type, resulting in a high residual nitrogenase activity. In a glnK background, the regulation of DRAT activity is similar to that seen in wild type. However, the regulation of DRAG activity is completely abolished in the glnK mutant; DRAG remains active even after NH 4 + addition, so there is no loss of nitrogenase activity. The results with this heterologous expression system have implications for DRAT-DRAG regulation in R. rubrum .