Elzora M. Jordan

Transcriptional activation of the F1F0 ATP synthase α-subunit initiator element by USF2 is mediated by p300

Abstract We have been studying the transcriptional regulation of the mammalian F 1 F 0 ATP synthase α-subunit gene ( ATPA ), a TATA-less initiator-containing gene. We have previously determined that the transcription factor, upstream stimulatory factor 2 (USF2), can activate the ATPA gene through an initiator element in the core promoter. Here, we demonstrate that the coactivator p300 interacts functionally with USF2 proteins to potentiate the activation of the ATPA initiator element by USF2. The physiological relevance of this interaction was shown in vivo by expression of the adenovirus E1A oncoprotein. Wild-type E1A, but not E1A mutants that lacked p300-binding sites, inhibited the USF2-dependent transactivation of the ATPA initiator element. Furthermore, overexpression of p300 could reverse the inhibitory effect of E1A. Collectively, our results indicate that the USF2-dependent transcriptional activation of the ATPA initiator element is mediated by p300.

Upstream stimulatory factor 2 stimulates transcription through an initiator element in the mouse cytochrome c oxidase subunit Vb promoter.

Upstream stimulatory factor (USF) is a basic helix-loop-helix-leucine zipper transcription factor that plays an important role in transcriptional activation and cell proliferation. In this article, we demonstrate that the mouse cytochrome c oxidase subunit Vb gene (Cox5b) can be transactivated by ectopic expression of USF2 through an initiator (Inr) element in the core promoter. Importantly, using a dominant-negative mutant of USF2, we demonstrate the role of endogenous USF2 proteins in the transcriptional activation of the Cox5b Inr. Domains of USF2 encoded by exon 4, exon 5 and the USF-specific region are important for maximum activation of the Cox5b Inr. Using the adenovirus E1A oncoprotein, we show that p300/CBP acts as a coactivator in the USF2-dependent activation of the Cox5b Inr. We also demonstrate that although expression of multifunctional regulatory factor, Yin Yang 1 (YY1), can stimulate transcription of the Cox5b Inr to a modest extent, expression of YY1 together with USF2 greatly reduces the level of activation of the Cox5b Inr. Furthermore, we show that the transcription factor, Sp1, represses both the YY1- and the USF2-dependent activation of the Cox5b Inr, indicating competition among Sp1, YY1, and USF2.

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

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.

Intermolecular and intramolecular transposition and transposition immunity in Tn3 and Tn2660

SummaryIntermolecular transposition of Tn2660 into pCR1 was measured at 30°C in recA− and recA+ hosts as between 2.6 and 5.5x10−3, a similar value to that previously found for Tn3. No cointegrate structures were found under conditions where 104 transposition events occurred. Immunity to intermolecular transposition of Tn2660, similar to that found for Tn3 was demonstrated by showing that the above transposition frequency was reduced by a factor of between 10−3 and 10−4 when a mutant Tn2660 (resulting in the synthesis of a temperaturesensitive β-lactamase) was present in the recipient plasmid. Intramolecular transposition of Tn3 was found to occur under the same conditions as previously demonstrated for Tn2660 giving rise to similar end products, in which the newly introduced Tn3 is oriented inversely to the resident Tn3 and the DNA sequence between the two transposons has been inverted. Thus, in all respects functional identity of the transposition activities of Tn3 and Tn2660 is shown, thereby identifying characteristics of intramolecular transposition that are not readily accommodated by current models of transposition.