DNase I footprinting of a PRNP promoter fragment extending from position -259 to +2. partial DNase I digestion was carried out either with (lane 2) or without (lane 1) HeLa cell nuclear extract. A dideoxy sequencing reaction with the same primer was included for positional reference (lanes 3-6). Two prominent footprints separated by three base pairs were designated prpB and prpA (brackets). The sequence of the DNase I protected domains are shown in the left panel.