A tyrosine-free medium for the selective growth of cells expressing phenylalanine hydroxylase activity

Abstract Tyrosine-free modified Ham's F-12 medium supplemented with charcoal-extracted serum permits the exclusive propagation of cultured cells containing detectable levels of phenylalanine hydroxylase. The selective properties of this medium have been verified with two phenylalanine hydroxylase-positive (H4-II-E-C3 and MH 1 C 1 ) and two phenylalanine hydroxylase-negative (HTC and BRL) cell lines. Although cocultivation experiments revealed that BRL cells could replicate slowly in the selective medium in the presence of sufficient numbers of H4-II-E-C3 cells, the former cells did not survive subcultivation in this medium at low cell inoculum ( 3 cells per 60 × 15-mm Petri dish). This tyrosine-free medium should be particularly effective in selecting for phenylalanine hydroxylase-positive somatic-cell hybrids under conditions of double selection where the phenylalanine hydroxylase-positive parental cell would not survive.