"YfeR", un nuevo regulador de la familia "LysR", está implicado en la respuesta al estrés en "Salmonella enterica" serovar Typhimurium

Abstract

Bacteria adapt to changes in their environment by modifying its pattern of gene expression. Adaptation to the medium osmolarity is one of the best characterized examples, however many of the well-known situations correspond to genes whose expression is induced when medium osmolarity increases. Previous work identified by random mutagenesis in "Salmonella enterica" serovar Typhimurium gene "yfeR", a hypothetical LysR-like regulator repressed at high osmolarity. This work is focused on the study of the model of regulation of YfeR. The sequence analysis of YfeR protein showed most of the common features of LysR family: an N-terminal conserved domain, 308 amino acids long, an anomalous Lys/Arg ratio, and homology with members of the LysR family. As for the majority of LysR regulators, YfeR negatively autoregulated its own transcription. In the promoter region of "yfeR" was located a sequence having characteristics of a LysR-type target consensus motif. Gel retardation assays demonstrated that YfeR binds specifically to this region. All these results clearly related YfeR to the LysR family of transcriptional regulators. About the osmoregulation of "yfeR" gene expression we confirmed, by indirect and direct methods (transcriptional fusion "yfer::lacZ" and RNasa protection assays, respectively), that its expression is repressed at high osmolarity. An ORF, "yfeH", was found oriented in the opposite direction to "yfeR", a common property of genes regulated by members of the LysR family. However, expression of "yfeH" gene is induced in stationary phase independently of the presence of YfeR and osmolarity conditions. Then we decided to search for other possible regulated genes by YfeR but not in adjacent position. Protein extracts of an "yfeR"mutant and wild type strains were analyzed by 2D electrophoresis. Some differences were found and two of them were identified as IbpA and Lrp. These results suggest that YfeR could be implied in a global regulation network related to environmental stimuli.