Question

The arginine biosynthetic genes in E. coli are found within an operon. Following exposure to a mutagen, an arginie auxotroph is generated. Where would you expect to find mutations leading to the phenotype? More than one site is possible.

Answer 1

Auxotrophs are those bacteria which can synthesize their food on their own when grown on a minimal media and do not require external supply of the essential nutreints. Although all types of bacteria contain these sequences, they might be silenced in some strains most probably due to silencing of the promoter regions. Thus, any mutation which activates these promoter regions would help the bacteria to express these genes which help them to synthesize their food on their own.

Hence, it is very likely that this mutation must have emerged in the promoter region of the gene responsible for synthesis of the nutrient and hence it might have taken place at more than one locations in the genome which encode for the nutrients.