REPRESSION OF TRANSCRIPTIONAL ENHANCER FACTOR-I AND ACTIVATOR PROTEIN-1-DEPENDENT ENHANCER ACTIVITY BY VASCULAR ACTIN SINGLE-STRANDED-DNA BINDING-FACTOR-2

Transcriptional repression of the murine vascular smooth muscle alpha- actin gene in fibroblasts results from the interaction of two sequence -specific single-stranded DNA binding activities (VACssBF1 and VACssBF 2) with opposite strands of an essential transcriptional enhancer fact or-1 (TEF-1) element (Sun, S., Stoflet, E. S., Cogan, J. G., Strauch, A. R., and Getz, M. J. (1995) Mol. Cell. Biol. 15, 2429-2436). Here, w e identify a sequence element located within a protein-coding exon of the gene that bears structural similarity with the TEF-1 enhancer. Thi s includes a 30-base pair region of purine-pyrimidine asymmetry encomp assing a perfect 6-base pair GGAATG TEF-1 recognition motif. Unlike th e enhancer, however, the exon sequence exhibits no TEF-1 binding activ ity nor does the pyrimidine-rich strand bind VACssBF1. However, VACssB F2 interacts equally well with the purine-rich strand of both the enha ncer and the exon sequence. To test the ability of VACssBF2 to indepen dently repress transcription, the exon sequence was placed upstream of a deletionally activated promoter containing an intact TEF-1 binding site. The exon sequence repressed promoter activity, whereas a mutant deficient in VACssBF2 binding did not. Moreover, VACssBF2 similarly re pressed activator protein-1-dependent transcription of a heterologous tissue factor promoter. These results suggest that VACssBF2 possesses an intrinsic ability to disrupt enhancer function independently of the enhancer-binding proteins involved.