Resonance assignments of sigma factor S binding protein Crl from Escherichia coli

During bacterial transcription, sigma (σ) factors reversibly bind to RNA polymerase (RNAP) and recognize specific promoter sequences to initiate the process. While different sigma factors are utilized under different external conditions, Sigma S (RpoS, σ^S), a stress-responding sigma factor, is activated when bacteria face external threats. σ^S, which has a much lower affinity to RNAP compared with sigma D (RpoD, σ⁷⁰), is controlled by a very complex network of regulatory factors. Crl protein, a transcriptional factor from Escherichia coli (E. coli, Ec), stimulates σ^S-dependent transcription by promoting the association of σ^S with core RNA polymerase. As an important regulator for σ^S, Crl is induced by low temperature, leading to an increased transcription rate of a subset of genes of the rpoS regulon under stress conditions or in stationary phase of growth. However, the underlying molecular mechanism for Crl/σ^S remains elusive. Here we describe the complete ¹H, ¹³C and ¹⁵N chemical shift assignments of Crl as the basis for NMR structure determination and interaction studies.