Transactivation properties of Gal4-fusion constructs containing truncated versions of p45: effect of A-kinase. The structure of p45¹ and the Gal4-fusion constructs containing variable amounts of N-terminal p45 sequences fused to the DNA binding domain of Gal4 are shown in (A); results of cotransfection experiments using these constructs in BHK cells are shown in (B). The indicated transactivator plasmid (5 ng) was cotransfected with the reporter pGAL4-Luc (100 ng), the control vector pRSV-βGal (50 ng), and either an expression vector for the C-subunit of A-kinase (pCMV-Cα, 50 ng, open bars) or empty vector (pRC/CMV, 50 ng, filled bars). Luciferase activity was normalized to β-galactosidase activity in each sample; the luciferase/β-galactosidase ratio obtained with the parent vector pSG424, which is lacking p45 sequences, was assigned a value of 1. Results represent the mean ± SD of three independent experiments.