The Gene Encoding the Cγ Catalytic Subunit of cAMP-Dependent Protein Kinase Is a Transcribed Retroposon

Three different catalytic isoforms of cAMP-dependent protein kinase have been identified (Cα, Cβ, and Cγ). We report the cloning and characterization of the human and rhesus monkey genes encoding the testis-specific Cγ subunit. The human Cγ gene is intronless with an open reading frame similar to the previously published cDNA sequence. The 3′ and 5′ flanking regions share high similarity with the Cα nontranslated regions (82%) also outside the regions corresponding to the Cγ cDNA. The human gene is flanked by anAlu-related sequence in the 5′-end and there are insertions of twoAlu-related sequences in the 3′ nontranslated region. The observation that the Cγ gene is intronless and colinear with Cα mRNA, together with the presence of remnants of a poly(A) tail and flanking direct repeats, indicates that the Cγ gene is a Cα-derived retroposon. The 5′ flanking region of this gene has a high G/C content and a putative TATA box situated at −138 compared to the translation initiation codon. Cloning and sequencing of a partial Cγ rhesus monkey gene demonstrate conservation of the sequence in primates. Northern analysis on isolated and fractionated human germ cells of testes from normal and estrogen-treated individuals demonstrates that the Cγ gene is expressed only in germ cells in the human testis. Our results indicate that the Cγ gene is a retroposon specifically transcribed in primate testicular germ cells.