Regulation of the Nuclear Gene That Encodes the α-Subunit of the Mitochondrial F0F1-ATP Synthase Complex ACTIVATION BY UPSTREAM STIMULATORY FACTOR 2

Abstract We have previously identified several positivecis-acting regulatory regions in the promoters of the bovine and human nuclear-encoded mitochondrial F0F1-ATP synthase α-subunit genes (ATPA). One of these cis-acting regions contains the sequence 5′-CACGTG-3′ (an E-box), to which a number of transcription factors containing a basic helix-loop-helix motif can bind. This E-box element is required for maximum activity of theATPA promoter in HeLa cells. The present study identifies the human transcription factor, upstream stimulatory factor 2 (USF2), as a nuclear factor that binds to the ATPA E-box and demonstrates that USF2 plays a critical role in the activation of theATPA gene in vivo. Evidence includes the following. Antiserum directed against USF2 recognized factors present in HeLa nuclear extracts that interact with the ATPApromoter in mobility shift assays. Wild-type USF2 proteins synthesized from expression vectors trans-activated theATPA promoter through the E-box, whereas truncated USF2 proteins devoid of the amino-terminal activation domains did not. Importantly, expression of a dominant-negative mutant of USF2 lacking the basic DNA binding domain but able to dimerize with endogenous USF proteins significantly reduced the level of activation of theATPA promoter caused by ectopically coexpressed USF2, demonstrating the importance of endogenous USF2 in activation of theATPA gene.