THE ROLE OF THE CORYNEBACTERIUM-GLUTAMICUM REL GENE IN (P)PPGPP METABOLISM

To investigate the metabolism of (p)ppGpp in amino-acid-producing cory neform bacteria, a PCR-based strategy using degenerate consensus oligo nucleotides was applied to isolate the rel gene of Corynebacterium glu tamicum ATCC 13032. The gene consists of 2283 nucleotides and encodes a protein of 760 amino acids with a molecular mass of 84.4 kDa. The am ino acid sequence revealed extensive similarities to the related prote ins RelA and SpoT of Escherichia coli, which are known to be involved in (p)ppGpp biosynthesis and degradation. The C. glutamicum rel gene i s located downstream of the apt gene encoding an adenine phosphoribosy ltransferase, and an ORF with similarities to dciAE, which represents part of a dipeptide transport system in E. coli. A C. glutamicum mutan t strain carrying a defined deletion in the rel gene was constructed. This mutant failed to accumulate (p)ppGpp in response to amino acid st arvation. When overexpressed in E. coli, the C. glutamicum rel gene wa s able to reverse growth defects caused by an overexpressed relA gene. It is proposed that the C. glutamicum rel gene encodes a bifunctional enzyme with (p)ppGpp synthetase and (p)ppGpp-degrading activities.