STRUCTURAL REQUIREMENTS FOR IN-VIVO MYOSIN-I FUNCTION IN ASPERGILLUS-NIDULANS

We have investigated the minimal requirements of the tail region for m yosin I function in vivo using the filamentous fungus Aspergillus nidu lans. The CL3 strain (McGoldrick, C. A., Gruver, C., and May, G. S. (1 995) J. Cell Biol. 128, 577-587) was transformed with a variety of myo A constructs containing mutations in the IQ, TH-1-like, SH3, and proli ne-rich domains by frameshift or in-frame deletions of the tail domain s. The resulting strains contained wild type myoA driven by the alcA p romoter and a mutant myoA driven by its endogenous promoter. This stra tegy allowed for selective expression of the wild type and/or mutant f orm of MYOA by the choice of growth medium. Proper septation and hypha l branching were found to be dependent on the interaction of the IQ mo tifs with calmodulin, as well as, the presence of its proline-rich dom ain, Additionally, a single proline-rich motif was sufficient for near ly wild type MYOA function. Most surprisingly, the SH3 domain was not essential for MYOA function. These studies expand our previous knowled ge of the function of MYOA to include roles in hyphal morphogenesis, s eptal wall formation, and cell polarity, laying the groundwork for mor e detailed investigations on the function of the various tail domains in MYOA.