The Escherichia coli guaB promoter (PguaB) is responsible for directing transcription of the guaB and guaA genes that specify the biosynthesis of the nucleotide GMP. PguaB is subject to growth rate-dependent control (GRDC), and possesses an UP element that is required for this regulation. In addition, PguaB contains a discriminator, three binding sites for the nucleoid-associated protein, FIS, and putative binding sites for the regulatory proteins DnaA, PurR and CRP. Here, we show that the CRP.cAMP complex binds to a site located over 100 bp upstream of the guaB transcription start site, where it serves to downregulate PguaB. The CRP-mediated repression of PguaB activity increases in media that support lower growth rates. Inactivation of the crp or cyaA genes, or ablation/translocation of the CRP site, relieves repression by CRP and results in loss of GRDC of PguaB. Thus, GRDC of PguaB involves a progressive increase in CRP-mediated repression of the promoter as the growth rate decreases. Our results also suggest that the CRP.cAMP complex does not direct GRDC at PguaB, and that at least one other regulatory factor is required for conferring GRDC on this promoter. However, PurR and DnaA are not required for this regulatory mechanism.