Column (a), ability of the wild type strain S1 (row (c)) and
Column (b), the inability of the GR6 pyrGmutant strain (row (c)) to
grow on minimal medium CD plates. Column (a), inability of the
wild type strain S1 (row (d)) and Column (b), ability of the GR6
pyrGmutant strain (row(d)) to growon minimal mediumCDplates
supplemented with uracil, uridine and 5-FOA.