Identification of a cryptic promoter in SPG4 exon 1. (a) Schematic representations of the firefly luciferase reporter constructs used. The position of the predicted Sp1 sites is indicated. (b) HeLa, SH-SY-5Y and HEK293 cells were cotransfected with the indicated constructs and with a CMV-Renilla luciferase plasmid. Cell lysates were prepared 24 hours post-transfection and the activity of the firefly luciferase was normalized to that of Renilla luciferase. For each construct at least three independent experiments were performed using different DNA preparations. (c) Mutation of each and both predicted Sp1 sites were generated in the S -207/+259 construct and tested in HeLa cells as described above (n = 3). Error bars represent standard error of the mean. The P-value of Student's t test is shown.