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Two sequence elements located at -111 to -100 base pairs and -70 to -50 base pairs in the 5'-flanking region of the bovine CYP11A gene and in closely related positions in CYP11A of other species contain G-rich regions that are similar to the consensus Sp1-binding site. These sequences bind the purified transcription factor Sp1 as well as nuclear proteins from mouse Y1 adrenal cells that interact with an antibody specific for Sp1. Both of these CYP11A sequences support basal and cAMP-dependent transcription of reporter gene plasmids transfected into Y1 cells, and mutations within the G-rich -111/-100-base pair sequence that reduce or eliminate the binding of Sp1-related Y1 nuclear proteins also markedly reduce cAMP-induced transcription. cAMP-dependent transcription supported by both CYP11A sequence elements is mediated by protein kinase A at levels comparable to that promoted by different cAMP-response sequences and transcription factors in other genes involved in steroidogenesis. These results indicate that ACTH-dependent regulation of cholesterol side chain cleavage cytochrome P450 levels in the adrenal cortex which is mediated through cAMP involves the ubiquitous transcription factor Sp1.