Activity of internal deletions within the full-length PRNP (-1593 to +134) promoter construct (column 1) in HeLa cells. Either binding domain prpA (column 4, dA) or prpB (column 5, dB), or both domains (column 6, dAB) were internally deleted. Deletions from the 5' end at restriction sites Bpm I (column 2, position -232) and Afe I (column 3, position -90) are shown for comparison. The activity of each deletion was expressed relative to the activity of the full-length promoter construct (100%). Each column shows the average of at least six independent experiments with standard deviation.