Drosophila neurotactin is a transmembrane glycoprotein with an apparent molecular mass of 135 x 10(3). Neurotactin is regionally expressed at the cellular blastoderm stage; later in embryogenesis the expression of the protein becomes restricted to cells of the peripheral and central nervous system. Immunocytochemical localization shows neurotactin protein at points of cell-cell contact. Using the anti-neurotactin monoclonal antibody BP-106, a neurotactin cDNA was isolated that encodes a 846 residue polypeptide. The chromosomal location of the neurotactin gene is 73C. The extracellular domain at the carboxyterminal end of the neurotactin protein shows a strong structural and sequence homology to serine esterases without retaining the amino acids forming the active center. Neurotactin therefore belongs to a growing group of proteins including Drosophila glutactin and thyroglobulins that are known to share this serine esterase protein domain motif without retaining the active center of the enzyme.