cAMP causes the dissociation of the inactive holoenzyme into a dimer of regulatory subunits bound to four cAMP and two free monomeric catalytic subunits.Second messenger cyclic AMP (cAMP)mediates diverse cellular responsesto external signals such as proliferation, ion transport, regulation of metabolismand gene transcription by activation of the cAMP-dependent proteinkinase (cAPK or PKA).Activation of transcription upon elevation of cAMP levels results from translocation of PKA to the nucleus where it phosphorylates the transcription factor cAMP response element binding protein (CREB) on serine 133 which in turn leads to TFIIB binding to TATA-box-binding protein TBP1, thus linking phospho-CREB to the pol II transcription initiation complex.
