Mutant alleles of mammalian myosin XVA cause profound congenital deafness DFNB3. In humans worldwide, mutations of MYO15A apepars to be the third most common mutated gene associated with deafness. Myosins are actin based molecular motors that have a conserved head (motor) and neck (light chain binding motifs) and highly divergent tail domains. The MYO15A tail contains several motifs that are candidates for protein interaction motifs. To date, isoform 1 of myosin XVa is the largest of all reported vertebrate myosins. The N-terminus of myosin XVa is composed of 1,220 residues. We previously demonstrated that isoform 1 is necessary for hearing (Nal et al., 2007). As a collaboration with extramural scientists, a mouse model has been developed that has a defective amino terminus which recapitulates the human phenotype (unpublished data). The identification of proteins that functionally interact with MYO15 may provide a means of determining the role of MYO15A in the auditory system. In addition, interacting proteins are themselves likely to play crucial roles in hearing and would be strong candidates for proteins encoded by other deafness loci. We are therefore using a yeast two hybrid system and MS screens to identify proteins that interact with the myosin XVA. Genes that encode poteins that interact with myosin XVA from these two screens will be further examined for biological relevance. Whirlin is one such partner of the tail domain of myosin XVa and is necessary for stereocilia elongation and staircase formation (Belyantseva et al. 2005). We are also characterizing the biophysical properties of myosin XVa.