The activity of a short and a long ART1 promoter fragment is upregulated during myotube formation. (A) Shown is the exon-intron structure of the mouse ART1 gene as described previously . Exons 1–5 are represented by boxes, introns by thin lines. Coding regions are indicated in black, non-coding regions in white. (B) A long (-1236/+36) and a short (-322/+37) fragment of the putative mouse ART1 promoter region (pART1-L: grey bars and pART1-S: black bars, respectively) was cloned into the pGL4.10 firefly luciferase reporter plasmid. C3H-10T 1/2 (Pg, MyoD-Mb, Mt) and C2C12 (Mb, Mt) cells were transfected with the plasmids and promoter activities were determined using the dual luciferase reporter assays normalized to renilla luciferase activity. Promoter activities are shown as fold activation respective to the pGL4.10 basal activity (pGL4.10 = 1). The data represent means ± S.D. of three independent experiments in triplicate. An arrow indicates the transcription start site numbered with +1 and 'luc' boxed indicates the firefly luciferase gene.