Shоwn is the yeаst biоsynthetic pаthwаy fоr production of the nucleobase adenine. Next to each arrow is the gene (in italics) that encodes the enzyme that catalyzes that step in the pathway. When P-ribosylamino imidazole (AIR) accumulates, it gets oxidized to form a red pigment that turns the yeast cells pink. Yeast cells with a mutation in which gene turn pink?