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 m uscle regulatory factors and ubiquitous Sp1 transcription factor are r equired in the initiation of the transcription of the chick betaTM gen e in muscle tissue. Our results also suggest that other factors may pa rticipate to this process.