Biosynthetic regulation of individual proteins in relA + and relA strains of Escherichia coli during amino acid starvation

Abstract

An isogenic pair of Escherichia coli mutants (relA ⁺ tufB valS ^ts and relA1 tufB valS ^ts) has been cultured at several temperatures to establish various degrees of limitation for valyl-tRNA synthetase. The biosynthetic rate of 16 identifiable proteins, most of which are components of the transcription and translation apparatus, was measured by pulse-labelling with [³⁵S]-methionine, followed by protein separation using two-dimensional gel electrophoresis (O'Farrell, 1975). No single pattern of response to amino acid starvation of biosynthetic rate was observed. EF-Ts, L12 and S6 were found to be under strong stringent and relaxed regulation; EF-G, EF-Tu-A and S1 are under strong stringent, but weak relaxed regulation; EF-Tu-B, α, VRS, IRS and ARS are under weak stringent and weak relaxed regulation; β is under weak stringent regulation and does not respond at all to relaxed conditions; the biosynthetic rate of a protein called stringent starvation protein is strongly stimulated, relative to other proteins, in the starved stringent strain.