Cloning and expression of an intron-less gene for AKAP 75, an anchor protein for the regulatory subunit of cAMP-dependent protein kinase IIβ

The A-Kinase Anchor Protein AKAP 75 (formerly designated bovine brain P75) is a particulate brain protein that avidly binds the regulatory subunit (RIIβ) of cAMP-dependent protein kinase IIβ (Bregman, D. B., Hirsch, A. H. and Rubin, C. S. (1991) J. Biol. Chem. 266, 7207-7213). The formation of stable AKAP 75 · RIIβ complexes provides a potential mechanism for targeting physiological signals carried by cAMP to specific effector sites within neurons and other brain cells. We have now cloned and characterized the AKAP 75 gene. Its coding sequence is novel and unexpectedly short (1284 base pairs) and contains no introns. When the AKAP 75 gene was transfected into HEK 293 cells, a new RIIβ-binding protein with an apparent M(r) of 75,000 accumulated. A high proportion (~65%) of the AKAP 75 gene product was excluded from the cytoplasm and was recovered in the 40,000 x g pellet derived from disrupted transfected cells. In contrast, cells transfected with a construct encoding 249 amino acids from the central and C-terminal regions of AKAP 75 produced an RIIβ-binding protein (apparent M(r) = 45,000) that was exclusively cytosolic. AKAP 75 is a novel protein composed of only 428 amino acid residues (M(r) = 47,878). A highly acidic C-terminal region mediates the binding of RIIβ (and cAMP-dependent protein kinase IIβ), whereas a positively charged N-terminal segment contains structural features that are essential for the association of AKAP 75 with the cytoskeleton and/or intracellular membranes.