DROSOPHILA SHAKING-B PROTEIN FORMS GAP-JUNCTIONS IN PAIRED XENOPUS OOCYTES

In most multicellular organisms direct cell-cell communication is medi ated by the intercellular channels of gap junctions. These channels al low the exchange of ions and molecules that are believed to be essenti al for cell signalling during development and in some differentiated t issues, Proteins called connexins, which are products of a multigene f amily, are the structural components of vertebrate gap junctions(1,2). Surprisingly, molecular homologues of the connexins have not been des cribed in any invertebrate. A separate gene family, which includes the Drosophila genes shaking-B and l(1)ogre, and the Caenorhabditis elega ns genes unc-7 and eat-5, encodes transmembrane proteins with a predic ted structure similar to that of the connexins(3-9). shaking-B and eat -5 are required for the formation of functional gap junctions(8,10). T o test directly whether Shaking-B is a channel protein, we expressed i t in paired Xenopus oocytes. Here we show that Shaking-B localizes to the membrane, and that its presence induces the formation of functiona l intercellular channels. To our knowledge, this is the first structur al component of an invertebrate gap junction to be characterized.