1) arsC evolved after araA/araB since a reducing environment existed pre-dating the necessity for the reductase activity encoded by arsC.
2) ArsA, arsB and arsC should be highly conserved given their ubiquity in all three domains.
3) Non-ATP dependent AraB should be structurally different from ATP-dependent AraB.
4) The phlyogenetic relationships between ara genes should reflect the 16S rRNA phylogenies.
1) arsC sequences are very dissimiliar between Archaea and bacteria. Indeed, sequences search do not recover any ArsC Archaea genes, although several species are known to contain them.
2) ArsA and arsB phylogenetically grouped with species in the Eubacteria, Archaea and Eukarya domains suggesting that other than structural constraints around the active site, there is much less conservation elsewhere.
3) The branches in the phylogenetic trees are very short indicating little conservation of sequence.
1)Do a thorough search for ArsC sequeneces. Most likely there will be new sequences online as interest in Archaean speicies is high.
2) Syntenic chromosome structure for the ars operon should be quite interesting since lateral gene exchange and homologous recombination have driven evolution of arsenate resistance across domains.
3) ArsA has an internal duplication of ATPase domains in most species investigated. It would be most interesting to explore this feature of gene structure.
1) Mutations have been documented in E coli. Biochemical analysis of the relationship of arsenate resistance to gene structure will clarify structural constraints.
2) Selection of arsenate resistance mutants, using recombinant plasmids with heterologous sequences are all techniques that are accessible to student research.
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