The muscle specific promoter of chick beta tropomyosin gene requires helix-loop-helix myogenic regulatory factors and ubiquitous transcription factors.

The chick beta tropomyosin (TM) gene has two alternative transcription initiation start sites which are used in muscle or non muscle tissue. A recombinant plasmid containing 805 nucleotides (nt) of the sequence upstream to the muscle CAP site driving the bacterial chloramphenicol acetyltransferase gene is sufficient for muscle specific expression. Of the two E boxes present in this construct, only the E box proximal to the CAP site is functional since deletion or mutation of this E box causes a decrease of CAT activity (about 40%). Separate mutation of Sp1 motifs also reduces the transcription driven by the 805nt fragment. Double mutation of E box and Sp1 motifs show that helix-loop-helix muscle regulatory factors and ubiquitous Sp1 transcription factor are required in the initiation of the transcription of the chick beta TM gene in muscle tissue. Our results also suggest that other factors may participate to this process.