In the budding yeast Kluyveromyces marxianus, adenylate cyclase is regulated by Ras protein(s) in vitro.

The presence of adenylate cyclase activity was first demonstrated in membrane fractions from the budding yeast Kluyveromyces marxianus. The enzyme showed a Mn(2+)- and Mg(2+)-dependent activity, with optimal pH at around 6 as observed in other yeast species. As in Saccharomyces cerevisiae, where adenylate cyclase is regulated by RAS1 and RAS2, we detected a guanyl nucleotide-dependent activity. Interestingly Y13-259 monoclonal antibody, raised against mammalian p21Ha-ras, inhibited Mg2+ plus GTP-gamma-S-dependent cAMP production, suggesting that the GTP binding proteins involved in adenylate cyclase regulation could be Ras proteins. The same antibody recognized on Western blot and immunoprecipitated a 40 kDa polypeptide from K. marxianus crude membranes. This polypeptide was not detected by an anti-RAS2 polyclonal antibody raised against S. cerevisiae RAS2 protein, suggesting that Ras proteins from the two species could be structurally different.