Effects of dual deletion of glnR and mtrA on expression of nitrogen metabolism genes in Streptomyces venezuelae

GlnR activates nitrogen metabolism genes under nitrogen-limited conditions whereas MtrA represses these genes under nutrient-rich conditions in Streptomyces. In this study, we compared the transcription patterns of nitrogen metabolism genes in a double deletion mutant ({Delta}mtrA-glnR) lacking both mtrA and glnR and in mutants lacking either mtrA ({Delta}mtrA) or glnR ({Delta}glnR). The nitrogen metabolism genes were expressed similarly in {Delta}mtrA-glnR and {Delta}glnR under both nitrogen-limited and nutrient-rich conditions, with patterns distinctly different from that of {Delta}mtrA, suggesting a decisive role for GlnR in the control of nitrogen metabolism genes and further suggesting that regulation of these genes by MtrA is GlnR-dependent. MtrA and GlnR utilize the same binding sites upstream of nitrogen metabolism genes, and we showed stronger in vivo binding of MtrA to these sites under nutrient-rich conditions and of GlnR under nitrogen-limited conditions, consistent with the higher levels of MtrA or GlnR under those respective conditions. In addition, we showed that both mtrA and glnR are auto-regulatory. Our study provides new insights into the regulation of nitrogen metabolism genes in Streptomyces.