Attempts to reconstruct the phenotypes of strains 2.3a and 2.3b from causative mutations. (A and B) To test the sufficiency of the identified causative mutations for strains 2.3a and 2.3b, beginning with the sin4Δ strain, FY3055, strains were constructed that contained each mutation singly (data not shown), as different combinations of double and triple mutants, and as the quadruple mutants. All plates contain galactose as the carbon source. Pictured is the highest 3AT concentration with strong 2.3a or 2.3b growth on day 4. (C) Northern analysis was done to measure HIS3 RNA levels in the reconstructed mutants and to compare the levels to that in the original polygenic mutants 2.3a and 2.3b.