A Corynebacterium glutamicum mutant with a defined deletion within the rpIK gene is impaired in (p)ppGpp accumulation upon amino acid starvation

The rpIK gene of Corynebacterium glutamicum ATCC13032 comprises 438 nucleotides and encodes a protein of 145 amino acids with a molecular mass of 15.3 kDa. The amino acid sequence revealed extensive similarities to the large ribosomal subunit protein L11 from several Gram-positive and Gram-negative bacteria. The C. glutamicum rpIK gene is located downstream of secE, representing part of the protein export apparatus, and of nusG, encoding a transcription antiterminator protein. The rpIK gene is followed by an ORF homologous to rpIA encoding the 50S ribosomal protein LI. Northern analysis revealed that transcription of the rpIK-rpIA cluster resulted in two different transcripts of 1.5 and 0.6 kb. The 1.5 kb transcript corresponds to the entire rpIK-rpIA cluster and the short transcript originates from the rpIK gene. A C. glutamicum rplK mutant strain carrying a 12 bp in-frame deletion within rplK, which resulted in the loss of the tetrapeptide Pro-Ala-Leu-Gly in the L11 protein, was constructed. The mutant failed to accumulate (p)ppGpp in response to amino acid starvation and exhibited an increased tolerance to the antibiotic thiostrepton. Evidently, the C. glutamicum rplK gene is required for (p)ppGpp accumulation upon nutritional starvation.