Molecular cloning of Odf3 encoding a novel coiled-coil protein of sperm tail outer dense fibers.

The outer dense fibers (ODF) are the main cytoskeletal structures of the sperm tail found in animals with internal fecundation. They consist of at least 14 polypeptides from which only a few are identified due to difficulties in isolation of the protein components. Here we report the isolation and molecular characterization of Odf3, encoding a novel protein of rat sperm ODF. Odf3 is transcribed in testes and more specifically in spermatids but it is also expressed in epididymides and brain suggesting a possible involvement in building of the cellular cytoskeleton. Odf3 encodes a putative protein of approximately 110 kDa. Secondary structure predictions indicated that ODF3 is a coiled-coil protein. The identification of coiled-coil proteins as constituents of outer dense fibers reveals a model for ODF formation.