lex A is an E. coli gene whose product regulates the transcription of certain ta
ID: 50275 • Letter: L
Question
lex A is an E. coli gene whose product regulates the transcription of certain target genes that are located at different positions in the bacterial chromosome. Identified target genes appear to be involved in DNA repair and recombination. Under normal conditions, the LexA protein binds near and represses transcription of target genes; however, when the cell experiences significant DNA damage caused by environmental mutagens, the LexA protein is inactivated and transcription of the target genes occurs. Your research objective is to identify all of the target genes repressed by the LexA protein. (Assume that you have access to a DNA microarray consisting of sequences representing each of the genes in the E. coli genome.) As the starting point for your work, you isolate a lexA mutant strain that produces no functional LexA protein.
Briefly describe an experiment that uses a functional genomics approach to identify all of the LexA target genes. Give the basic steps of the experiment and show how it would allow you to achieve your objective.
Explanation / Answer
Answer:
Detail procedure can be Obtained from the below journal, please go through it,
The cyanobacterial genes lexA, recA and ruvB were analysed in Synechocystis PCC6803, which is shown here to be more radiation resistant than the other unicellular model strain Synechococcus PCC7942. We found that cyanobacteria do not have an Escherichia coli-type SOS regulon. The Synechocystis lexA and recA promoters were found to be strong and UV insensitive, unlike the ruvBpromoter, which is weak and UV-C inducible. Yet, lexA and recA are regulated by UV-C, but the control is negative and occurs at the post-transcriptional level.
Two novel conserved elements were characterized in the lexA promoter:
(i) an unusually long crucial box 5-TAAAATTTTGTATCTTTT-3 (64, 47); and (ii) a negatively acting motif 5-TAT GAT-3 (42, 37). These elements were not found in therecA promoter, which appeared to be unusually simple in harbouring only a single crucial element (i.e. the canonical 10 box). RuvB, operating in recombination-dependent cellular processes, was found to be dispensable to cell growth, whereas LexA and RecA appeared to be critical to cell viability. Using DNA microarrays, we have identified 57 genes with expression that is altered, at least twofold, in response to LexA depletion. None of these genes is predicted to operate in DNA metabolism, arguing against the involvement of LexA in the regulation of DNA repair. Instead, most of the LexA-responsive genes were known to be involved in carbon assimilation or controlled by carbon availability. Consistently, the growth of the LexA-depleted strain was found to be strongly dependent on the availability of inorganic carbon.
http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2958.2004.04100.x/full
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