H-043. A LysR-type Transcriptional Regulator of Caulobacter crescentus Is Involved in Oxidative Stress Response

V. S. Braz, J. F. da Silva Neto, V. C. S. Italiani, M. V. Marques;
Univ. of São Paulo, São Paulo, BRAZIL.

Caulobacter crescentus is a free-living Alphaproteobacterium that has eleven predicted LysR-type transcriptional regulators (LTTRs). LysR family proteins typically contain an N-terminal helix-turn-helix motif and require a bound co-inducer to activate transcription of target genes. Previously, a mutant strain with a miniTn5lacZ transposon inserted into a gene that encodes a LTTR in Caulobacter crescentus was isolated, which was susceptible to cadmium, zinc, iron and hydrogen peroxide. A null mutant strain, where the gene was exchanged by a streptomycin resistance cassette, was obtained (SP2012) and it also showed to be sensitive to hydrogen peroxide, confirming the phenotype previously observed. This strain was more sensitive to superoxide (paraquat) than the wild type strain, but it did not show to be more sensitive to organic hydroperoxide (t-butyl hydroperoxide), as verified by growth inhibition zone assays. The transcriptional start site of this gene was determined by primer extension analysis and its promoter was cloned in front of the lacZ reporter gene. β-Galactosidase activity assays, performed in the wild type and mutant strains, indicated that this gene is twofold induced by hydrogen peroxide and when cells enter stationary phase, and that it is negatively auto-regulated. Moreover, this regulator is essential for the expression of the divergent gene, which encodes a hypothetical protein. A model is proposed to explain the antagonistic double regulation.