Sperm antigen 6 is the murine homologue of the Chlamydomonas reinhardtii central apparatus protein encoded by the PF16 locus

A cDNA encoding sperm antigen 6 (Spag6), the murine homologue of the Chlamy domonas reinhardtii PF16 protein-a component of the flagella central appara tus-was isolated from a mouse testis cDNA library, The cDNA sequence predic ted a 55.3-kDa polypeptide containing 8 contiguous armadillo repeats with 6 5% amino acid sequence identity and 81% similarity to the Chlamydomonas PF1 protein. An antipeptide antibody generated against a C-terminal sequence r ecognized a 55-kDa protein in sperm extracts and localized Spag6 to the pri ncipal piece of permeabilized mouse sperm tails. When expressed in COS-1 ce lls, Spag6 colocalized with microtubules, The Spag6 gene was found to be hi ghly expressed in testis and was mapped using the T31 radiation hybrid pane l to mouse chromosome 16, Mutations in the Chlamydomonas PF16 gene cause fl agellar paralysis. The presence of a highly conserved mammalian PF16 homolo gue (Spag6) raises the possibility that Spag6 plays an important role in sp erm flagellar function.