Inhibition of hydrogenase synthesis by DNA gyrase inhibitors in Bradyrhizobium japonicum

Abstract

Derepression of an uptake hydrogenase in Bradyrhizobium japonicum is dependent on a microaerophilic environment. Addition of DNA gyrase inhibitors during derepression of hydrogenase specifcally prevented expression of the hydrogenase enzyme. Antibodies to individual hydrogenase subunits failed to detect the protein after derepression in the presence of inhibitors, although there was no general inhibition of protein syntbesis. The general pattern of proteins synthesized from 14C-labeled amino acids during derepression was not significantly different whether proteins were labeled in the presence or in the absence of gyrape inhibitors.In contrast, if transcriptiop or translation was inhibited by addition of inhibitors of thowe functions, virtually no proteins were labeled during derepression. This indicated that most of the 14C-labeled proteins were synthesized de novo during derepression, synthesis of most proteins was unaffected by gyrase inhibitors, and the dependence of hydrogenase synthesis on gyrase activity was a specific one.

Osmotic repression of anaerobic metabolic systems in Escherichia coli

“…Aside from its response to osmotic stress, DNA supercoiling was also involved in the regulation of anaerobic gene expression (13,32,33,52). The relationship between gyrasedependent and FNR-dependent anaerobic regulation has been observed by investigators in different laboratories.…”

Regulation of the fixA gene and fixBC operon in Bradyrhizobium japonicum

“…In E. coli and Salmonella typhimurium it is well known that alterations in the superhelical nature of the chromosomal DNA can have a tremendous effect on the expression of a large number of genes, in either a positive or a negative way (16). A similar phenomenon has recently been described in the case of the uptake hydrogenase genes of B. japonicum (34). (ii) The lac fusions present on a multicopy plasmid might titrate out one of the factors required for nif and fix gene expression (such as NifA or NtrA) and thus cannot be activated to full extent.…”

Common cis-acting region responsible for transcriptional regulation of Bradyrhizobium japonicum hydrogenase by nickel, oxygen, and hydrogen

“…Previously, our laboratory provided evidence that DNA gyrase is required for the expression of hydrogenase in free-living B. japonicum (26). When gyrase inhibitors such as novobiocin, coumermycin, or nalidixic acid were introduced to the cells at the onset of derepression in a microaerobic environment, hydrogenase was not synthesized.…”

“…When gyrase inhibitors such as novobiocin, coumermycin, or nalidixic acid were introduced to the cells at the onset of derepression in a microaerobic environment, hydrogenase was not synthesized. Thus, it was proposed that 02 regulates hydrogenase at the transcriptional level (26).…”