Domain switching between hrpR and hrpS affects the regulatory function of the hybrid genes in Pseudomonas syringae pv. phaseolicola.
Abstract In prokaryotes, a diverse set of physiological processes is regulated by transcription factors which belong to the well-conserved, enhancer-binding protein (EBP) family. These regulatory proteins function together with the alternate sigma factor (sigma(54)). Structurally, the EBPs are characterized by a central activator domain, containing the recognition motif for the RNA polymerase/sigma(54) complex (Esigma(54)), and the C-terminal domain, containing a DNA-binding helix-turn-helix motif. A regulatory system of the EBP type also exists in Pseudomonas syringae, where it controls the expression of genes required for the induction of disease symptoms and resistance responses in plants. The system consists of the two genes, hrpR and hrpS, which belong to the hrp (hypersensitive response and pathogenicity) gene cluster. The two genes show a high degree of structural and sequence similarities, but function at different positions in the hrp regulatory cascade of the bean pathogen Pseudomonas syringae pv. phaseolicola. In this paper, we were interested in the basis of the difference in specificity between hrpR and hrpS. The functional specificities of the two domains of hrpS and hrpR were analysed by domain switching. Complementation analyses with the hybrid genes and retardation experiments with the protein products showed significant differences between the respective domains of hrpS and hrpR.
Schuster
M
M
Institute of Botany, Department of Cytology and Genetics, University of Vienna, Rennweg 14, A-1030 Vienna, Austria.
Grimm
C
C