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An evolutionary model for hisA and hisF genes. Right-most panel is the evolutionary model that we propose and discuss in the text concerning hisA and hisF origin and evolution. Panels on the left are: the first and the second quarters (top) and two single (β/α) modules of the HisA protein from Thermotoga maritima which illustrates the structural similarities from which we derived our model. The quarters have a structural alignment with only 1.2 Å of RMS on 104 alpha carbons.
