Characterization of the relA/spoT homologue slr1325 ( synrsh) of the cyanobacterium Synechocystis sp.PCC6803

Abstract:

Abstract:［Objective］ Nucleotide guanosine-3'，5'-( bis) pyrophosphate ( ppGpp ) synthesized by ( ppGpp ) synthesase RelA or bifunctional ppGpp synthase / degradase RelA / SpoT，mediates bacterial stringent response to various stressful conditions． Here we characterized the slr1325 ( syn-rsh ) gene encoding a RelA / SpoT homolog ( Syn-RSH ) of the cyanobacterium Synechocystis sp． PCC6803． ［Methods］We performed phenotypic complement test using Escherichia coli strain with( p) ppGpp-synthesis defect to determine Syn-RSH function( s) ，and employed chromatographic analysis of32 Plabeled cellular mononucleotides to detect the accumulation of ppGpp in Escherichia coli strains expressing Syn-RSH and in Synechocystis sp． PCC6803． ［Results］ Syn-RSH expression in E． coli relA / spoT double mutant was able to restore the cell growth arrest; Chromatographic analysis of32 P-labeled cellular mononucleotides revealed that Syn-RSH expression resulted in the synthesis of ppGpp in E． coli strain with relA and spoT mutant mutation． Additionally，Synechocystis cells accumulated a low level of ppGpp under laboratory growth conditions． ［Conclusion］Syn-RSH possesses ppGpp synthase /degradase activities，and ppGpp is required for Synechocystis cell viability under normal growth conditions．