2 E-BOXES ARE THE FOCAL POINT OF MUSCLE-SPECIFIC SKELETAL-MUSCLE TYPE-1 NA-EXPRESSION( CHANNEL GENE)

We have characterized a group of cis-regulatory elements that control muscle-specific expression of the rat skeletal muscle type 1 sodium ch annel (SkM1) gene. These elements are located within a 3.1-kilobase fr agment that encompasses the 5'-flanking region, first exon, and part o f the first intron of SkM1. We sequenced the region between -1062 and +311 and determined the start sites of transcription; multiple sites w ere identified between +1 and +30. The basal promoter (-65/+11) lacks cell-type specificity, while an upstream repressor (-179/-65) confers muscle-specific expression. A positive element (+49/+254) increases mu scle-specific expression, Within these broad elements, two E boxes pla y a pivotal role. One E box at -31/-26 within the promoter, acting in part through its ability to bind the myogenic basic helix-loop-helix p roteins, recruits additional factor(s) that bind elsewhere within the SkM1 sequence to control positive expression of the gene. A second E b ox at -90/-85 within the repressor controls negative regulation of the gene and acts through a different complex of proteins. Several of the se cis-regulatory elements share both sequence and functional similari ties with cis-regulatory elements of the acetylcholine receptor delta- subunit; the different arrangement of these elements may contribute to unique expression patterns for the two genes.