Two-component regulatory systems
Springer Online Journal Archives 1860-2000
Abstract Expression of the pilin gene, pilA, of Pseudomonas aeruginosa requires the alternative sigma factor, σ54, and also two other transcriptional regulators encoded by the pilS and pilR genes. These two linked genes, which have been identified by transposon insertion mutagenesis, share significant amino acid sequence homology with members of the two-component family of regulators. The transcriptional regulator, PilR, has been described previously. PilS, a 37285 Dalton protein, shares significant homology with the protein kinase sensors of the two-component regulatory family. PilS, however, has no hydrophobic domains which might be membrane-spanning alpha-helices, suggesting that PilS is a cytoplasmic protein. Characterization of the pilS gene revealed that when overexpressed in Escherichia coli by the bacteriophage T7 promoter it specifies a protein of approximately 40000 daltons, corresponding to the molecular weight of Pi1S predicted from the deduced amino acid sequence. Deletion analysis of the pilS promoter fused to a promoterless lacZ gene further showed that a significant region upstream of pilS is essential for expression of pilS and pilR, suggesting a need for transcriptional activation. The pilA promoter can be activated in E. coli but only when PilR and σ54 are present. This work suggests that the Pi1S activation signal is received in the bacterial cytoplasm, and that the mechanism of Pi1S/PiIR-mediated signal transduction resulting in activation of the pilin gene promoter is likely to be similar to that of other two-component systems.
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