M-CAT BINDING-FACTOR, A NOVEL TRANS-ACTING FACTOR GOVERNING MUSCLE-SPECIFIC TRANSCRIPTION

The cardiac troponin T (cTNT) promoter contains a highly muscle specific distal promoter element capable of conferring muscle-specific transcription from a heterologous TATA box-transcription initiation site. Three sequence motifs within this distal promoter element are conserved in the promoter and regulatory regions of many sarcomeric protein genes. Mutational analysis demonstrated that homologies to two of these conserved motifs (CArG/CBAR and MEF 1) were not required for activity of cTNT promoter-marker gene constructs in transfected embryonic skeletal muscle cells. In contrast, disruption of either or both copies of the conserved M-CAT motif (5'-CATTCCT-3') inactivated the cTNT promoter in these cells. Both M-CAT motifs were protected from DNase I cleavage in solution footprint assays by an M-CAT binding factor (MCBF) present in nuclear extracts from embryonic muscle tissue. M-CAT mutations that inactivated the cTNT promote also disrupted MCBF binding, indicating that MCBF may be a key trans-acting factor required for muscle-specific expression of the cTNT promoter. MCBF also bound to the M-CAT motif in the distal promoter region of the skeletal α-actin gene, suggesting that it may play a role in the regulation of this and perhaps other muscle genes that contain M-CAT motifs.