Growth phase and growth rate regulation of the rapA gene, encoding the RNApolymerase-associated protein RapA in Escherichia coli

The Escherichia coli rapA gene encodes the RNA polymerase (RNAP)-associated protein RapA, which is a bacterial member of the SWI/SNF helicase-like pro tein family. We have studied the rapA promoter and its regulation in vivo a nd determined the interaction between RNAP and the promoter in vitro. We ha ve found that the expression of rapA is growth phase dependent, peaking at the early log phase. The growth phase control of rapA is determined at leas t by one particular feature of the promoter: it uses CTP as the transcripti on-initiating nucleotide instead of a purine, which is used for most E. col i promoters. We also found that the rapA promoter is subject to growth rate regulation in vivo and that it forms intrinsic unstable initiation complex es with RNAP in vitro. Furthermore, we have shown that a GC-rich or discrim inator sequence between the -10 and +1 positions of the rapA promoter is re sponsible for its growth rate control and the instability of its initiation complexes with RNAP.