A new species of enkephalin precursor mRNA with a distinct 5′‐untranslated region in haploid germ cells

To elucidate the primary structure of preproenkephalin (A) mRNA expressed by haploid germ cells (round spermatids) in rat testis, we have screened a lambda gt11 cDNA library for preproenkephalin cDNA inserts. The largest cDNA insert contained a protein-coding sequence encoding 269 amino acid residues as well as 327 and 309 bases of the 5'- and 3'-untranslated regions, respectively. The protein-coding region plus 3'-untranslated region of the mRNA was over 99% homologous to that of brain preproenkephalin mRNA, whereas the 5'-untranslated region contained a distinct sequence including a partial sequence of intron A of the preproenkephalin gene [(1984) J. Biol. Chem. 259, 14301-14308; (1984) J. Biol. Chem. 259, 14309-14313]. Northern blot analysis using a 5'-end-specific probe showed that this type of preproenkephalin mRNA exists exclusively in the germ cells.