INFLUENCE OF STRINGENT AND RELAXED RESPONSE ON EXCRETION OF RECOMBINANT PROTEINS AND FATTY-ACID COMPOSITION IN ESCHERICHIA-COLI

In contrast to stringent (relA(+)) cells of Escherichia coli, relaxed (relA) cells excreted recombinant proteins (beta-lactamase, interferon alpha 1) into the culture medium during amino acid limitation. Compar ative analyses of overall fatty acid composition in relA(+) cells and relA cells were performed and revealed that, in wild-type cells, drast ic alterations occurred during the stringent response. The portion of saturated fatty acids (C16:0) and the fractions of cyclopropane fatty acids (C17(cyc) and C19(cyc)) increased whereas the portions of unsatu rated fatty acids (C16:1 and C18:1) decreased. In cells of the relaxed mutant, no significant changes in the overall composition of the fatt y acids were observed after the onset of amino acid limitation. These results indicate that a change in fatty acid composition of membrane l ipids after starvation of cells may be responsible for the prevention of loss of cellular proteins into the culture medium in stringent cont rolled cells of Escherichia coli.