FUNCTIONAL INTERACTIONS BETWEEN TRANSLATION, TRANSCRIPTION AND PPGPP IN GROWING ESCHERICHIA-COLI

Strains with a relA mutation together with three different alleles of spoT were used to study the effects of different levels of ppGpp on pr oduction time for beta-galactosidase, transcriptional polarity and rea dthrough of a stop codon by near-cognate tRNA or a suppressor tRNA. Th e influences of an rpsL(S12) allele and a miaA mutation, together givi ng decreased efficiency of translation, as well as an rpoB mutation, c oding for an altered RNA polymerase, were also investigated. The spoT alleles which give total deficiency for ppGpp, or a level which is inc reased several-fold (Sarubbi et al. (1988) Mel. Gen. Genet. 213, 214-2 22), had at the most a marginal effect on the production time for a be ta-galactosidase molecule or translational misreading of a nonsense mu tation. The efficiency of an amber tRNA suppressor is not affected by ppGpp in strains with an otherwise wildtype translational machinery. T hese data suggest that ppGpp does not influence directly the translati onal process in vivo. Instead, ppGpp is found to interfere with transc riptional readthrough in a manner which is dependent on the rpsL224, m iaA, as well as the rpoB mutations. Similarily, bacterial growth is af fected by ppGpp in a manner which is dependent on properties of both t he transcriptional and translational apparatus together. It is suggest ed that the primary effect of ppGpp is on transcriptional readthrough, but this effect is modified by translational/transcriptional coupling .