Electrophoretic analysis of proteins from Phycomyces mutants with abnormal tropisms

Certain phototropism mutants of Phycomyces blakesleeanus show defective bending responses (tropisms) to stimuli besides light, such as gravity, wind, and barriers. These so-called "stiff" mutants are affected in four genes (madD to madG). Using two-dimensional gel electrophoresis, we have analyzed polypeptides from microsomal and soluble fractions obtained from the wild type, four single mutants, and six double mutants affected in all pairwise combinations of the four genes. Consistent differences in spot patterns for madE and madF mutants were found in microsomal fractions but not in soluble fractions. In madE mutants, two spots designated E1 (52 kDa, pI 6.65) and E2 (50 kDa, pI 6.65) were altered. E1 appeared denser in the wild type than in the madE mutants, while the reverse was true for E2. The spots E1 and E2 are probably under regulatory control by madE, perhaps involving posttranslational modification. A protein spot, F1 (53 kDa, pI 6.1), was present on the wild-type gels but absent from all gels for madF mutants. The F1 polypeptide probably represents the madF gene product.