REL606 and REL607 (the ancestral strains of the E. coli long-term evolution experiment) differ by a single point mutation in the araA gene. This mutation was originally present in REL606. It makes an excellent neutral marker for evolution and competition experiments. REL607 was selected as a spontaneous arabinose-utilizing revertant from REL607. Most spontaneous revertants selected from a strain with the REL606 araA allele have the REL607 allele, but other mutations at this amino acid are also known to confer an Ara+ phenotype.
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