REGULATION OF MURINE CYTOCHROME-OXIDASE VB GENE-EXPRESSION IN DIFFERENT TISSUES AND DURING MYOGENESIS - ROLE OF A YY-1 FACTOR-BINDING NEGATIVE ENHANCER

The mouse cytochrome oxidase (COX) Vb promoter contains three sequence motifs with partial or full consensus for YY-1 and GTG factor binding and a CArG box, located between positions -480 and -390, Individually , all three motifs stimulated transcription of the TKCAT promoter, and bound distinctly different proteins from the liver and differentiated C2C12 nuclear extracts, Collectively, these motifs, together with the downstream flanking sequence, -378 to -320, suppressed the transcript ion activity of heterologous promoters, thymidine kinase-chloramphenic ol acetyltransferase (TKCAT) and COXIV/CAT, The transcription activiti es of both TKCAT and COXIV/CAT constructs were induced 3-4-fold during induced myogenesis of C2C12 cells, The downstream CArG-like motif bin ds transcription factor YY-1, while the upstream YY-1-like motif binds to a yet unidentified factor. Go-expression with intact YY-1, but not that lacking the DNA binding domain suppressed the transcriptional ac tivity. Mutations targeted to the CArG-like motif abolished the suppre ssive effect of the negative enhancer and the inducibility of the prom oter during myogenic differentiation. Our results suggest that the act ivity of the negative enhancer may determine the level of expression o f the COX Vb gene in different tissues.