Growth phase-dependent regulation of nuoA-N expression in Escherichia coliK-12 by the Fis protein: upstream binding sites and bioenergetic significance

The expression of the nuoA-N operon of Escherichia coli K-12, which encodes the proton-pumping NADH dehydrogenase I is modulated by growth phase-depen dent regulation. Under respiratory growth conditions, expression was stimul ated in early exponential, and to a lesser extent in late exponential and s tationary growth phases. The stimulation in the early exponential growth ph ase was not observed in fis mutants, which are deficient for the growth pha se-responsive regulator Fis. Neither the alternative sigma factor RpoS nor the integration host factor (IHF) are involved in growth phase-dependent re gulation of this operon. When incubated with nuo promoter DNA, isolated Fis protein formed three retarded complexes in gel mobility experiments. DNase I footprinting identified three distinct binding sites for Fis, 237 bp (fi s1), 197 bp (fis2) and 139 bp (fis3) upstream of the start of the major tra nscript of nuoA-N, T1. The protein concentrations required for half-maximal binding to fis1, fis2 and fis3 were about 20 nM, 40 nM and 100 nM Fis, res pectively. The II-IF protein bound 82 bp upstream of the start of transcrip t T2 with a half-maximal concentration for binding of 50 nM. Due to the gro wth phase-dependent regulation by Fis, the synthesis of the coupling NADH d ehydrogenase I is increased relative to that of the non-coupling NADH dehyd rogenase II during early exponential growth. This ensures higher ATP yields under conditions where large amounts of ATP are required.