Progesterone-induced oocyte maturation is thought to involve the inhibition of an oocyte adenylyl cyclase and reduction of intracellular cAMP. Our previous studies demonstrated that injection of inhibitors of G protein βγ complex induces hormone-independent oocyte maturation. In contrast, over-expression of Xenopus Gβ1 (xGβ1), alone or together with bovine Gγ2, elevates oocyte cAMP and inhibits progesterone-induced oocyte maturation. To further investigate the mechanism of Gβγ-induced oocyte maturation, we generated a mutant xGβ1, substituting Asp-228 for Gly (D228G). An equivalent mutation in the mammalian Gβ1 results in the loss of its ability to activate adenylyl cyclases. Indeed, co-injection of xGβ1D228G with Gγ2 failed to increase oocyte cAMP or inhibit progesterone-induced oocyte maturation. To directly demonstrate that oocytes contained a Gβγ-regulated adenylyl cyclase, we analyzed cAMP formation in vitro by using oocyte membrane preparations. Purified brain Gβγ complexes significantly activated membrane-bound adenylyl cyclase activities. Multiple adenylyl cyclase isoforms were identified in frog oocytes by PCR using degenerate primers corresponding to highly conserved catalytic amino acid sequences. Among these we identified a partial Xenopus adenylyl cyclase 7 (xAC7) that was 65% identical in amino acid sequence to human AC7. A dominant-negative mutant of xAC7 induced hormone-independent oocyte maturation and accelerated progesterone-induced oocyte maturation. Theses findings suggest that xAC7 is a major component of the G2 arrest mechanism in Xenopus oocytes. © 2005 Wiley-Liss, Inc.