ROLE OF THE ESCHERICHIA-COLI FADR REGULATOR IN STASIS SURVIVAL AND GROWTH PHASE-DEPENDENT EXPRESSION OF THE USPA, FAD, AND FAB GENES

The increased expression of the uspA gene of Escherichia coli is an es sential part of the cell's response to growth arrest, We demonstrate t hat stationary-phase activation of the uspA promoter is in part depend ent on growth phase-dependent inactivation or repression of the FadR r egulator, Transcription of uspA is derepressed during exponential grow th in fadR null mutants or by including the fatty acid oleate in the g rowth medium of FadR(+) cells, The results of DNA footprinting analysi s show that FadR binds downstream of the uspA promoter in the noncodin g region, Thus, uspA is a member of the fadR regulon, All the fad-lacZ fusions examined (fadBA, fadL, and fadD) are increasingly expressed i n stationary phase with kinetics similar to that of the increased expr ession of uspA. In contrast, beta-galactosidase levels decrease during stationary phase in a fabA-lacZ lysogen, consistent with the role of FadR as an activator of fabA. The growth phase-dependent increased and decreased transcription of fad genes and fabA, respectively, is depen dent on the status of the fadR gene, Cells carrying a mutation in the FadR gene (fadRS219N) that makes it nonderepressible exhibit a weak st ationary-phase induction of uspA and fad genes, In addition, cells car rying fadRS219N sun ive long-term stasis poorly, indicating that FadR- dependent alterations in fatty acid metabolism are an integral and imp ortant part of the adaptation to stationary phase.