Characterization of a promoter element required for transcription in myocardial cells.

Transcription of the chicken cardiac troponin T (cTNT) gene in myocardial cells requires upstream sequences not required for expression of this gene in embryonic skeletal muscle cells. Deletion analysis shows that the segment between nucleotides -247 and -201 (numbered relative to the transcription initiation site at +1) is capable of conferring cardiac specific expression to a "minimal" cTNT promoter. The cardiac element within this segment contains at least two essential subregions: one residing upstream of position -215, which bears no homologies to known transcription elements, and an A/T-rich segment residing between positions -215 and -201. Conserved M-CAT motifs within the cTNT minimal promoter which are required for activity in skeletal muscle cells are also required for activity in myocardial cells, suggesting an interaction between the upstream cardiac element and proximal promoter elements. Gel-shift experiments demonstrate interaction between the upstream portion of the cardiac element and factor(s) present in the nuclei of cardiac and non-cardiac tissues. Thus, additional cis and trans factors are required for transcription of the cTNT gene in myocardial cells which are not required for expression in skeletal muscle cells.