In vivo role of the relA+ gene in regulation of the lac operon

Abstract

Under conditions of amino acid limitation, ,B-galactosidase was produced at a 70-fold higher rate in a relAU strain than in an isogenic relA strain of Escherichia coli K-12. Under identical conditions with the reLA+ and reLA strains carrying various lac promoter mutations, rates of 8-galactosidase synthesis in relA+ (relative to reUA) ranged from 26-fold higher (promoter mutant P'13) to only 5fold higher (promoter mutant PrL8uv5). This promoter specificity was independent ofstrain background and the means ofeliciting amino acid limitation. Addition of cyclic AMP to the growth medium altered the reLA+/reLA difference for ,8galactosidase synthesis from the wild-type lac promoter. The experiments suggest that the reUA/reLA difference in lac expression arises primarily at the point of transcription initiation. The results are discussed in relation to recent in vitro data showing a promoter-specific guanosine 5'-diphosphate 3'-diphosphate stimulation of lac transcription (P.

The function of a ribosomal frameshifting signal from human immunodeficiency virus‐1 in Escherichia coli

“…Our wild type lacZ* controi shows a marked decrease in p-galactosidase synthesis during limitation for each of tiie amino acids tested. This response is typical of relA ~ cells, and is primarily caused by a dependence of /acZtranscription on ppGpp during amino acid limitation (Primakoff and Artz, 1979;Yangefa/., 1979;Primakoff, 1981;Foieyefa/., 1982), compounded by errors in transiation at some hungry codons (reviewed by Gallant, 1979;Cashe! and Rudd, 1987;Parker, 1989).…”

Independence of cyclic AMP and relA gene stimulation of glycogen synthesis in intact Escherichia coli cells

“…Although an increase in the concentration of cyclic AMP stimulates the synthesis of all four of these enzymes, additional observations by Primakoff (30) suggest that the alternative dependent mechanism, relA --cyclic AMP --enzyme synthesis, does not appear to function via an increase in cyclic AMP concentration. He showed that the differential rate of P-galactosidase synthesis was 70-fold greater in a relA' strain during amino acid starvation than in its corresponding relA mutant, but the basal cellular level of cyclic AMP was not increased by amino acid starvation in either strain.…”

“…Other E. coli systems that show relA-cyclic AMP dual regulation and that have been studied by other workers are induction of acetohydroxy acid synthase (18), tryptophanase (35), ,-galactosidase (30), and ribulokinase (36). These four studies appear to rule out the particular dependent mechanism cyclic AMP --relA --enzyme synthesis for those systems, because cyclic AMP stimulated enzyme synthesis in the absence of the relA gene (or in the case of tryptophanase and ribulokinase, in the absence of the relA gene product ppGpp).…”

“…Based on these studies, it appears that glycogen synthesis, like a number of other metabolic processes in E. coli, is subject to dual control by relA gene function and by cyclic AMP.The phenomenon of dual control by the relA gene and cyclic AMP and the question of whether these two controls act independently has intrigued investigators for some time. To date, studies on induction of acetohydroxy acid synthase (18), tryptophanase (35), P-galactosidase (30,31), and ribulokinase (36) have not answered this question. In contrast, the studies presented here provide strong evidence that the dual controls of glycogen synthesis by cyclic AMP and by the relA gene are independent.When the stringent response is triggered, growth slows and cellular glycogen accumulation increases (5,25,33).…”

The gene encoding dihydrolipoyl transacetylase from Azotobacter vinelandii

“…Finally, a comment should be made on the late expression of E2 protein and activity noticed in these experiments. One of the factors that might be responsible for this, could be the dependence of the E2 gene from the vector-encoded lac2 promoter; this promoter is known to be stimulated by guanosine 3'-diphosphate 5'-diphosphate (ppGpp) [20]. The concentration of ppGpp is low at high growth rates and is highly raised in a process called 'stringent response' [21] in the stationary phase of the growth cycle or when specific nutrients, like amino acids, are depleted.…”