 In exponential phase, "crp" mutants exhibit high levels of "rpoS" expression, suggesting that cAMP-CRP inhibits "rpoS" transcription.Upon entry into stationary phase, on the other hand, cAMP-CRP may upregulate "rpoS" transcription (Hengge-Aronis, 2002).While these observations may explain the seemingly dual nature of the cAMP-CRP binding sites, they require an explanation of phase-dependent selection of cAMP-CRP site activation to fully account for the contradictory data.