Rica Dela Cruz
Mentor: Dr. Monica Chander
SoxR is a redox-sensitive transcriptional dual regulator and activator protein. Homologs of this protein, in addition to the specific DNA sequences it binds, exist in various bacterial species. Traditionally, SoxR has been known to be an oxidative stress-defense protein, such as in the enteric bacterium, E. coli. In the presence of oxidative stress agents, SoxR’s characteristic iron-sulfur clusters become oxidized inducing a conformational change. This allows the protein to bind to a specific DNA promoter site to activate the expression of certain genes, which in turn produce various antioxidant proteins. Unlike E. coli, however, studies in other bacterial species have suggested that SoxR may play a role in the transport and/or modification of small molecules within the cell. For example, it has recently been found that SoxR regulates the efflux of the redox-active antibiotic, pyocynin, produced by the bacteria, Pseudomonas aeruginosa.
Analogous to P. aeruginosa, the soil bacterium, Streptomyces coelicolor, also seems to show a possible link between SoxR and one of the redox-active antibiotic it produces, actinorhodin. Though, this has only been shown phenotypically. DNA sequences homologous to the consensus sequence of the SoxR binding site have been found in promoter regions of S. coelicolor genes, SCO2478 and SCO4266. It is hypothesized that SoxR may either be activating or inhibiting the expression of SCO2478 and SCO4266 in the presence of endogenous actinorhodin. Gel shift assays do show that SoxR can bind to these regions in vitro. However, how SoxR binds and its downstream mechanisms are still unknown.
Other consensus sequences of the SoxR binding site have also been found in regions upstream of the ecaA, ecaB, and ecaC genes of S. coelicolor. One goal is to find out whether SoxR does bind to these regions. This will be answered by the analysis of gel shift assays. Another goal is to find out whether SoxR functions to activate or inhibit the expression of these genes: SCO2478, SCO4266, and possibly the eca genes. Thus, quantitative RT-PCR and microarrays using both wild type and mutant SoxR strains of S. coelicolor will be analyzed.