PROMOTER ELEMENTS AND TRANSCRIPTIONAL CONTROL OF THE CHICKEN BETA-TROPOMYCIN GENE

The chicken beta tropomyosin (beta TM) gene has two alternative transc ription start sites (sk and nmCAP sites) which are used in muscle or n on muscle tissues respectively. In order to understand the mechanisms involved in the tissue-specific and developmentally-regulated expressi on of the beta TM gene, we have analyzed the 5' regions associated wit h each CAP site. Truncated regions 5' to the nmCAP site were inserted upstream to the bacterial chloramphenicol acetyltransferase (CAT) repo rter gene and these constructs were transfected into avian myogenic an d non myogenic cells. The maximum transcription is driven by the CAT c onstruct (-168/+216 nt) in all cell types. Previous deletion analysis of the region 5' to the beta TMskCAP site has indicated that 805 nt co nfer myotube-specific transcription. In this work, we characterize an enhancer element (-201/-68 nt) which contains an E box(-177), a varian t CArG box(-104) and a stretch of 7Cs (-147). Mutation of any of these motifs results in a decrease of the myotube-specific transcriptional activity. Electrophoretic mobility shift assays indicate that these ci s-acting sequences specifically bind nuclear proteins. This enhancer f unctions in an orientation-dependent manner.