In vivo transcription of escherichia coli genes coding for ribosomal rna ribosomal proteins and subunits of rna polymerase influence of the stringent control system
Maher, D.L.; Dennis, P.P.
Molecular and General Genetics 155(2): 203-212
The synthesis of RNA and protein components of the ribosome is subject to stringent control. Elicitation of stringent or relaxed control occurs following limitation of aminoacylated tRNA in isogenic relA+ and relA- strains, respectively. The transcription of rRNA genes and of 3 additional mRNA producing segments of the bacterial chromosome were examined. These segments code, respectively, for 15 ribosomal proteins (r-protein) and the .alpha. subunit of RNA polymerase, 4 50S r-proteins, and the .beta. and .beta.' subunits of RNA polymerase. The 1st segment is located near 72 min but the 2nd and 3rd segments are contiguous with each other and located near 88 min. When the relA+ strain was limited for valyl tRNA the unusual nucleotide guanosine tetraphosphate (ppGpp) accumulates and transcription of genes coding for rRNA and r-proteins was reduced; transcription of the genes coding for the .beta. and .beta.' subunits of RNA polymerase was not affected. When the relA- strain was limited, ppGpp failed to accumulate and the transcription of rRNA and r-protein genes was enhanced, but transcription of the .beta. and .beta.' genes was not enhanced. Apparently, the stringent control system directly or indirectly regulates the genes coding for RNA and protein components of the ribosome at the level of transcription. The influence of this control system on the transcription of the 2 distinct and separate clusters of r-protein genes was identical. The transcription of genes for the .beta. and .beta.' subunits of RNA polymerase was distinctly different from transcription of r-protein genes and not subject to stringent control.