Issues

Cover picture: A tribute to Dr. Norton B. Gilula and his contributions to cell biology and the field of intercellular communication. Shown at the left is a freeze-fracture image of a mammalian gap junction recorded by Dr. Gilula in the early 1970's. At the right is a freeze-fracture image of a gap junction formed by a recombinant form of the cardiac gap junction protein (alpha1 connexin or Cx43) (Unger, V.M., N.M. Kumar, N.B. Gilula, and M. Yeager. 1999. J. Struct. Biol. 128:98-105). Electron cryo-microscopy and image analysis of the crystalline gap junctions yielded a projection map at 7-Å resolution (bottom), which showed a ring of transmembrane alpha-helices that lines the aqueous pore and a second ring of alpha-helices in contact with the membrane lipids (bottom) (Unger, V.M., N.M. Kumar, N.B. Gilula, and M. Yeager. 1997. Nature Struct. Biol. 4:39-43). Three-dimensional image reconstruction revealed that each hemichannel or connexon is formed by 24 alpha-helices (gold rods) (Unger, V.M., N.M. Kumar, N.B. Gilula, and M. Yeager. 1999. Science. 183:1176-1180). The two white boxes represent the membranes of the two cells that are coupled by the gold gap junction channel. The connexons within each membrane dock end-to-end and span the extracellular gap, thereby forming a conduit for intercellular exchange of ions and metabolites. Computer graphics by Michael E. Pique and Mark Yeager using AVS software.