Isolation and characterization of a haploid germ cell-specific novel complementary deoxyribonucleic acid; Testis-specific homologue of succinyl CoA: 3-oxo acid CoA transferase

We have isolated a cDNA clone encoding a mouse haploid germ cell-specific p rotein from a subtracted cDNA library. Sequence analysis of the cDNA reveal ed high homology with pig and human heart succinyl CoA:3-oxo acid CoA trans ferase (EC 2.8.3.5), which is a key enzyme for energy metabolism of ketone bodies. The deduced protein consists of 520 amino acid residues, including glutamate 344, known to be the catalytic residue in the active site of pig heart CoA transferase and the expected mitochondrial targeting sequence enr iched with Arg, Leu, and Ser in the N-terminal region. Thus, we termed this gene scot-t (testis-specific succinyl CoA:3-oxo acid CoA transferase), Nor thern blot analysis, in situ hybridization, and Western blot analysis demon strated a unique expression pattern of the mRNA with rapid translation excl usively in late spermatids. The scot-t protein was detected first in elonga ted spermatids at step 8 or 9 as faint signals and gradually accumulated du ring spermiogenesis. It was also detected in the midpiece of spermatozoa by immunohistochemistry. The results suggest that the scot-t protein plays im portant roles in the energy metabolism of spermatozoa.