Using native gel electrophoresis, we have discovered that Bcy1p, the regulatory subunit of the cAMP-dependent protein kinase, associates in a multi-protein complex as cells approach stationary phase. We have determined the size of this native complex to be approximately 230 kDa. The catalytic subunits (Tpk1, 2, or 3) are not part of the complex, since a complex of approximately equal size is formed in cells lacking the TPK genes. In addition, the complex is stable in the presence of cAMP, in contrast to the predicted dissociation of a Tpk-Bcy1 holoenzyme. We are using cAMP-affinity chromatography and immunoprecipitation to purify the complex and to analyze its components. As a complementary approach, we are cloning genes that interact with Bcy1p using the two-hybrid system. Results of these approaches will be presented.