INTERACTIONAL CLONING OF THE 84-KDA MAJOR OUTER DENSE FIBER PROTEIN ODF84 - LEUCINE ZIPPERS MEDIATE ASSOCIATIONS OF ODF84 AND ODF27

The study of mammalian sperm tail outer dense fibers (ODF), a structur e of unknown function, is hampered by the insoluble nature of ODF prot eins and the availability of only one cloned component, Odf27. We repo rt here the first use of the Odf27 leucine zipper as bait in a yeast t wo-hybrid screen to isolate a novel testis-specific protein whose inte raction with Odf27 depends critically on the Odf27 leucine zipper. We find that the novel gene, 111-450, encodes a product that localizes to ODF as determined by fluorescence microscopy and immunoelectron micro scopy and that the gene 111-450 product is identical to the major ODF protein, Odf84. Interestingly, Odf84 contains two C-terminal leucine z ippers, and we demonstrate that all leucine residues in the upstream l eucine zipper are required for interaction with Odf27, demonstrating t he strategic validity of our approach. The use of the yeast screening approach to isolate leucine zipper containing proteins should be usefu l in other systems, and our findings have implications for ODF structu ral models.