Cover photograph (Copyright © 2001, American Society for Microbiology. All rights reserved.): A model structure of ankyrin repeats from RFXANK (residues 88 to 243) with the mutated leucine at position 195 in the inner helix of the third ankyrin repeat (asterisk) that causes the bare lymphocyte syndrome in the FZA patient. In the ribbon diagram (top) are highlighted side chains of exposed variable residues at the tips of the four -hairpin loops. In the space-filling model (bottom), RFXAP binds to the -hairpin loops and the inner helix of the third ankyrin repeat, which are colored orange. Arrows point from the NH₂ to the COOH terminus of the protein. (See related article on page 5566.)