On the role of cyclic AMP and the Fnr protein in Escherichia coli growing anaerobically

Two-dimensional gel electrophoretic analysis of Escherichia coli proteins: influence of various anaerobic growth conditions and the fnr gene product on cellular protein composition

Two-dimensional gel electrophoresis was used to examine the response of the cellular proteins of Escherichia coli to various anaerobic growth conditions and to the presence or absence of a functional Fnr protein. The steady-state levels of 125 polypeptides were found to vary in either a positive or negative manner, with many polypeptides being affected under a number of conditions. A large number (21) of the anaerobically inducible polypeptides were shown to be totally independent of the presence of Fnr while 22 were shown to be reduced in a fnr mutant under all anaerobic growth conditions tested. A total of 8 proteins were shown to be reduced in a fnr mutant only in aerobically grown cells indicating that the Fnr protein has a function in the presence of oxygen. This was further confirmed by the observation that 15 anaerobically inducible polypeptides were also found to show an increase in aerobically grown cells, however, only in a fnr strain. This latter finding implies that Fnr may also exhibit repressor function. This effect of Fnr-dependent repression was also observed with several polypeptides in anaerobically grown cells.