Promoter elements and transcriptional control of the chicken 0 tropomycin gene

Abstract

The chicken (3 tropomyosin (/3TM) gene has two alternative transcription start sites (sk and nmCAP sites) which are used in muscle or non muscle tissues respectively. In order to understand the mechanisms involved in the tissue-specific and developmentally-regulated expression of the /3TM gene, we have analyzed the 5 ' regions associated with each CAP site. Truncated regions 5 ' to the nmCAP site were inserted upstream to the bacterial chloramphenicol acetyl-transferase (CAT) reporter gene and these constructs were transfected into avian myogenic and non myo-genic cells. The maximum transcription is driven by the CAT construct (-168 / + 216 nt) in all cell types. Previous deletion analysis of the region 5 ' to the /JTMskCAP site has indicated that 805 nt confer myotube-specific transcription. In this work, we char-acterize an enhancer element (- 201 /-68 nt) which contains an E box (-177) , a variant 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 c/s-acting sequences specifically bind nuclear proteins. This enhancer functions in an orientation-dependent manner