Three different catalytic isoforms of cAMP-dependent protein kinase have been identified (C alpha, C beta, and C gamma). We report the cloning and characterization of the human and rhesus monkey genes encoding the testis-specific C gamma subunit. The human C gamma 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 C alpha nontranslated regions (82%) also outside the regions corresponding to the C gamma cDNA. The human gene is flanked by an Alu-related sequence in the 5'-end and there are insertions of two Alu-related sequences in the 3' nontranslated region. The observation that the C gamma gene is intronless and colinear with C alpha mRNA, together with the presence of remnants of a poly(A) tail and flanking direct repeats, indicates that the C gamma gene is a C alpha-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 C gamma 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 C gamma gene is expressed only in germ cells in the human testis. Our results indicate that the C gamma gene is a retroposon specifically transcribed in primate testicular germ cells.