in purine-requiring strain of escherichia coli k-12 defective in purine nucleoside phosphorylase ( pur , pup ) mutants ( designated apt ) have been obtained that are resistant to 2,6-diaminopurine on guanine-containing medium and incapable to utilize adenine for their growth at 42degreesc , but they are still sensitive to the analogue and can utilize adenine at 28degreesc .
C0034140
purine
C0001407
adenine