Testicular protein Spag5 has similarity to mitotic spindle protein deepestand binds outer dense fiber protein Odf1

Outer dense fibers (ODF) and the fibrous sheath (FS) are major cytoskeletal structures in the mammalian sperm tail. The molecular mechanisms underlyin g their morphogenesis along the axoneme or their function are poorly unders tood. Recently, we reported the cloning and characterization of Odf2, a maj or ODF protein, and Spag4, an axoneme-binding protein I by Virtue of their strong interaction with Odf1, the 27 kDa major ODF protein. We proposed a c rucial role for leucine zippers in molecular interactions during sperm tail morphogenesis., Here we report the cloning and characterization of a novel gene, Spag5, which encodes a 200 kDa testicular protein that interacts str ongly with Odf1. Spag5 is transcribed and translated in pachytene spermatoc ytes and spermatids. it bears 73% similarity with the mitotic spindle prote in Deepest of unknown function. We identified two putative leucine zippers in the C-terminal part of the Spag5 protein, the downstream one of which is involved in interaction with Odf1. interestingly, these motifs are present in Deepest. These results highlight the importance of the leucine zipper i n sperm tail protein interactions. (C) 2001 Wiley-Liss, Inc.