Effect of point mutations on the activity of the cyclin A1 promoter. (A) After introducing mutations into potential transcription factor binding sites of the cyclin A1 promoter (335-bp fragment), luciferase constructs were transfected into KCL 22 cells that express high levels of c-myb (Fig 3). Bars represent the mean and SEM of at least 3 independent experiments. (B) The wild-type cyclin A1 reporter construct or the myb 1 site mutation of the cyclin A1 promoter was cotransfected with either c-myb or empty vector into CV-1 cells. These experiments were performed using the Dual Luciferase Assay system and the pRL-SV40 vector for standardization.