Understanding the Function of SoxR in Streptomyces coelicolor by Mutational Analysis

Posted May 12th, 2010 at 1:17 pm.

Yang Gao

Mentor: Dr. Monica Chander

SoxR is a transcriptional activator that has been extensively characterized in E. coli. In E. coli, SoxR is part of the defense mechanism used by the bacterium to protect itself from oxidative stress caused by drugs such as paraquat, and nitric oxide (NO). The chemical stresses are detected by SoxR via its iron sulfur ([2Fe-2S]) clusters. In the presence of oxidative stress, SoxR activates the expression of another transcriptional activator, SoxS, which in turn activates the expression of more than 40 genes that are responsible for reducing the stresses. The SoxR protein, and the specific DNA sequence it binds, is conserved throughout many other species of bacteria.

One of the species that possesses the homolog of the SoxR protein is Streptomyces coelicolor, a soil bacterium that is more complex than E. coli. One aspect of its complexity is that S. coelicolor produces and secretes secondary metabolites such as antibiotics into its surroundings to eliminate its competitors. It is hypothesized that SoxR in this organism functions to protect S.coelicolor from one such antibiotic, actinorhodin. This hypothesis is based on the fact that, while there is no soxS homolog in S. coelicolor, the conserved DNA sequence to which SoxR binds is found in the promoter regions of two genes, SCO2478 and SCO4266. These two genes are believed to be involved in detoxifying actinorhodin in S. coelicolor.

In order to elucidate the physiological role of SoxR in S.coelicolor, I will construct a soxR null mutant in S. coelicolor. Since SoxR is hypothesized to mediate self-toxicity against actinorhodin, the soxR mutation has the potential of being lethal to the organism. To circumvent this potential problem, the soxR deletion will be made in both the wild type strain (M145), as well as a mutant strain that does not produce actinorhodin (M512). Northern analysis carried out on the soxR mutant strain will allow us to verify that SoxR regulates SCO2478 and SCO4266, and will reveal the function of SoxR in S. coelicolor.

Filed under: 2008,Chander, Dr. Monica,Gao, Yang by Ann Dixon

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