myoA motor mutants are viable but display subtle growth defects. (A) Expression of S199T, E428V, and E445K-MYOA protein in A. nidulans strains. Protein extraction and analysis were performed as previously described (34). MYOA proteins were detected by using an affinity-purified polyclonal MYOA antibody (8). (B) Growth of wild-type and myoA motor mutant A. nidulans strains streaked on agar plates and incubated for 2 days at 37°C. (C) Differential interference contrast microscopy reveals that the initiation of hyphal growth on liquid medium is delayed in the myoA motor mutant strains. S199T cells also exhibit aberrant swollen hyphae and extensive vacuolization, whereas E428V and E445K hyphae display these effects to a lesser degree. (D) Quantification of radial growth of wild-type, S1992, E428V, and E445K strains on agar plates at 37°C. All of the mutants show a 2-h lag in hyphal emergence, whereas S199T also exhibits a decreased rate of radial growth as compared with the wild-type control strain. Approximately 50 independent colonies were measured for each time point. (E) myoA motor mutants exhibit delayed germination and decreased rates of hyphal elongation as compared with a wild-type control strain when grown in liquid culture at 37°C. Values plotted are the means measured for ≈50 independent germlings.