Distinct roles of the Drosophila ninaC kinase and myosin domains revealed by systematic mutagenesis.

The Drosophila ninaC locus encodes a rhabdomere specific protein (p174) with linked protein kinase and myosin domains, required for a wild-type ERG and to prevent retinal degeneration. To investigate the role for linked kinase and myosin domains, we analyzed mutants generated by site-directed mutagenesis. Mutation of the kinase domain resulted in an ERG phenotype but no retinal degeneration. Deletion of the myosin domain caused a change in the subcellular distribution of p174 and resulted in both ERG and retinal degeneration phenotypes. Temperature-sensitive mutations in the myosin domain resulted in retinal degeneration, but no ERG phenotype. These results indicated that the ERG and retinal degeneration phenotypes were not strictly coupled suggesting that the myosin domain has multiple functions. We propose that the role of the kinase domain is to regulate other rhabdomeric proteins important in phototransduction and that the myosin domain has at least two roles: to traffic the kinase into the rhabdomeres and to maintain the rhabdomeres.