Evidence for high molecular weight proteins in arthropod gap and smooth septate junctions

The proteins that make up arthropod gap and septate junctions have not been identified with any certainty. Several candidate proteins for both types o f junctions have been proposed in the literature, but there has been no agr eement on any of these. Arthropod gap junctions do not label with antibodie s to vertebrate gap junction connexins; it thus appears that unrelated prot eins form these rather similar structures. Gap junctions in Manduca sexta m idgut epithelium are unusual since they function only during the molt and a re non-functioning during the larval instars, We have developed a preparati on from this tissue that is highly enriched in both gap and smooth septate junctions when examined by electron microscopy. SDS-PAGE gels of this prepa ration have two major protein bands, at 75 and 90 kDa, The presence of gap junctions correlates best with the 75 kDa protein and smooth septate juncti ons with the 90 kDa protein. Further, the 75 kDa band is stained by an anti body to a putative gap junction protein from C, elegans, We propose that th e 75 kDa protein is a major structural component of gap junctions in Manduc a sexta midgut epithelium and that the 90 kDa protein forms the smooth sept ate junctions.