Mutations in the no-mechanoreceptor-potential A (nompA) gene, which eliminate transduction in Drosophila mechanosensory organs, disrupt contacts between neuronal sensory endings and cuticular structures. nompA encodes a transmembrane protein with a large, modular extracellular segment that includes a zona pellucida (ZP) domain and several plasminogen N-terminal (PAN) modules. It is specifically expressed in type I sense organs of the peripheral nervous system by the support cells that ensheath the neuronal sensory process. A green fluorescent protein (GFP)-NompA fusion protein is localized to the dendritic cap, an extracellular matrix that covers the ciliary outer segment of the sensory process and that shows organizational defects in nompA mutants. The structure and location of NompA suggest that it forms part of a mechanical linkage required to transmit mechanical stimuli to the transduction apparatus.