Regulatory subunit of the cyclic AMP-dependent protein kinase (PKA), an effector of the Ras/cAMP pathway. Inhibits PKA activity in the absence of cAMP. cAMP activates PKA and promotes growth and proliferation in response to good nutrient conditions. Together with ZDS1, provides a negative feedback control on the cell wall integrity-signaling pathway by acting as a negative regulator of MAP kinase SLT2/MPK1. The inactive holoenzyme of cAMP-dependent protein kinase is a tetramer, composed of 2 regulatory subunits (R, encoded by BCY1) and two catalytic subunits (C, encoded by the 3 partially redundant TPK1, TPK2, and TPK3 genes). Activation by cAMP causes dissociation of the holoenzyme, producing 2 active catalytic monomers C and a regulatory dimer R(2). Cytoplasmic when phosphorylated. Nuclear when not phosphorylated. The inhibitor sequence (IS) is a substrate recognition motif that docks to the active site cleft of the catalytic subunit rendering the holoenzyme inactive. Binding of cAMP to the 2 tandem cyclic-nucleotide binding domains (CNB-A and CNB-B) induces a conformational change in BCY1, causing the interaction surface with the catalytic subunit to be destroyed and eventually the dissociation of the R dimer from the C subunits. Phosphorylated by YAK1 in response to glucose starvation. Phosphorylated by MCK1 at Thr-129 upon TOR complex 1 (TORC1) inhibition. Thr-129 phosphorylation activates BCY1 to inhibit PKA. TORC1 inhibits phosphorylation of RxxS/T sites but has no effect on Ser-145 phosphorylation. The phosphorylation sites can be clustered in several groups, all localized in the N-terminal part. The first cluster termed cluster I (CI) is located close to the N-terminus and includes Ser-3, Ser-4 and Ser-9 (PubMed:11134339, PubMed:12704202). The second includes Ser-68, Ser-70, Ser-74, Ser-77, Ser-79, Ser-81, Ser-83, and Ser-84. This cluster of phosphorylation sites, termed cluster II (CII), is important for BCY1 cytoplasmic localization and function (PubMed:11134339, PubMed:12704202, PubMed:20702584). The third cluster of phosphorylated residues consists of Thr-144, Ser-145, Ser-147, Thr-150, and Thr-160. This cluster falls within or near the so-called autoinhibitory domain where the catalytic subunit of PKA autophosphorylates the highly conserved Ser-145 to inhibit BCY1 (PubMed:20702584). A last cluster of phosphorylated residues included Thr-129, Ser-130, and Thr-131 and is termed cluster III (CIII). Sites in CIII (and to a lesser extent in CII) are hyperphosphorylated in response to rapamycin (PubMed:20702584). Present with 4280 molecules/cell in log phase SD medium. Belongs to the cAMP-dependent kinase regulatory chain family.