The linotte mutant was isolated on the basis of its learning and memory deficit. Interestingly, linotte individuals carrying a null mutation are viable, indicating that the linotte gene is not required for vital functions. We show here that the linotte gene encodes a putative receptor tyrosine kinase, homologous to the human protein RYK. These products are unique among receptor tyrosine kinases, since they possess a short extra cellular domain, and a modified intracellular catalytic domain. In particular, the subdomains directly involved in ATP binding and phosphotransfer reaction display remarkable variations. These results suggest that linotte is part of a novel signal transduction cascade involved in learning and memory.