Regulation of the Escherichia coli K5 capsule gene cluster: Evidence for the roles of H-NS, BipA, and integration host factor in regulation of group 2 capsule gene clusters in pathogenic E-coli

The expression of Escherichia coil group 2 capsules (K antigens) is tempera ture dependent, with capsules only being expressed at temperatures above 20 degrees C. Thermoregulation is at the level of transcription, with no dete ctable transcription at 20 degrees C. Using the E. coli K5 capsule gene clu ster as a model system, we have shown that the nucleoid-associated protein H-NS plays a dual role in regulating transcription of group 2 capsule gene clusters at 37 and 20 degrees C. At 37 degrees C H-NS is required for maxim al transcription of group 2 capsule gene clusters, whereas at 20 degrees C H-NS functions to repress transcription. The BipA protein, previously ident ified as a tyrosine-phosphorylated GTPase and essential for virulence in en teropathogenic E. coli, was shown to play a similar role to H-NS in regulat ing transcription at 37 and 20 degrees C. The binding of integration host f actor (IHF) to the region 1 promoter was necessary to potentiate transcript ion at 37 degrees C and IHF binding demonstrated by bandshift assays. The I HF binding site was 3' to the site of transcription initiation, suggesting that sequences in the 5' end of the first gene (kpsF) in region 1 may play a role in regulating transcription from this promoter at 37 degrees C. Two additional cis-acting sequences, conserved in both the region 1 and 3 promo ters, were identified, suggesting a role for these sequences in the coordin ate regulation of transcription from these promoters. These results indicat e that a complex regulatory network involving a number of global regulators exists for the control of expression of group 2 capsules in E. coli.