Relationship between guanosine tetraphosphate and accuracy of translation in Salmonella typhimurium

Abstract

In bacteria a high level of mistranslation is observed in amino acid starved rel-, but not rel+, strains, and mistranslation can be studied qualitatively by means of "stuttering" experiments in two-dimensional protein gels. It has been suggested that the low level of mistranslation that occurs in rel+ strains is assured by guanosine 5'-diphosphate 3'-diphosphate (ppGpp), a nucleotide whose intracellular concentration greatly increases in rel+ cells under amino acid starvation. In the present study the relationship between level of ppGpp and mistranslation was analyzed by performing stuttering experiments in amino acid starved bacteria that contained either high or low levels of ppGpp. Three strains of Salmonella typhimurium were used in these experiments: a relA+ hisT+ strain (TA997), a relA+ hisT strain (TA1001), and a relA hisT strain (PD2). These strains were first characterized with respect to macromolecular syntheses and ppGpp levels under exponential growth and under amino acid starvation. Both rel+ strains exhibited stringent control over RNA synthesis. ppGpp accumulated to high levels when TA997 was starved for either of three amino acids. Starvation of TA1001 for histidine did not cause accumulation of ppGpp, whereas starvation for lysine and arginine produced high levels of ppGpp. Extracts from the three strains, obtained either under exponential growth or under amino acid starvation, were then subjected to two-dimensional electrophoretic anaylsis: mistranslation was observed whenever ppGpp was absent. In particular, starvation of TA1001 for histidine resulted in high mistranslation frequencies, while under lysine and arginine starvation mistranslation was undetectable, regardless of whether the cells were rel+ or rel-.(ABSTRACT TRUNCATED AT 250 WORDS)