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Synthetic growth phenotypes of Escherichia coli lacking ppGpp and transketolase A ( tktA ) are due to ppGpp‐mediated transcriptional regulation of tktB
Author(s) -
Harinarayanan Rajendran,
Murphy Helen,
Cashel Michael
Publication year - 2008
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.2008.06317.x
Subject(s) - stringent response , transketolase , biology , operon , rpos , beta galactosidase , escherichia coli , biochemistry , rpob , transcriptional regulation , lac operon , genetics , gene , enzyme , promoter , gene expression , 16s ribosomal rna
Summary Many physiological adjustments to nutrient changes involve ppGpp. Recent attempts to deduce ppGpp regulatory effects using proteomics or gene profiling can rigorously identify proteins or transcripts, but the functional significance is often unclear. Using a random screen for synthetic lethals we found a ppGpp‐dependent functional pathway that operates through transketolase B (TktB), and which is ‘buffered’ in wildtype strain by the presence of an isozyme, transketolase A (TktA). Transketolase activity is required in cells to make erythrose‐4‐phosphate, a precursor of aromatic amino acids and vitamins. By studying tktB ‐dependent nutritional requirements as well as measuring activities using P talA‐tktB ′‐ lacZ transcriptional reporter fusion, we show positive transcriptional regulation of the talA‐tktB operon by ppGpp. Our results show the existence of RpoS‐dependent and RpoS‐independent modes of positive regulation by ppGpp. Both routes of activation are magnified by elevating ppGpp levels with a spoT mutation ( spoT ‐R39A) defective in hydrolase but not synthetase activity or with the stringent suppressor mutations rpoB ‐A532Δ or rpoB ‐T563P in the absence of ppGpp.