FIG. 5.

UBF phosphorylation mediates SL1 recruitment to the rDNA promoter. (A) DNase I digestion of UBF and hypophosphorylated UBF on the coding strand of the human rDNA promoter with UCE and CORE region as indicated on the left. Shown are protection patterns with no protein added (lanes 1, 2, 5, and 6) or with increasing amounts of either UBF (lanes 3 and 4) or dephosphorylated UBF (lanes 7 and 8). (B) Footprinting analysis was performed as described for panel A with both forms of UBF in the presence of 1 μg of SL1. Shown are results with naked DNA only (lanes 1, 2, 7, 8, 9, 10, 15, and 16), UBF (lanes 3 and 4), AP-treated UBF (lanes 11 and 12), increasing amounts of UBF with SL1 (lanes 5 and 6), and increasing amounts of AP-treated UBF with SL1 (lanes 13 and 14). The region of DNA protected by UBF is indicated by bracket A, while SL1 extended footprinting is indicated by bracket B (UCE) and bracket B′ (CORE). Hypersensitive sites at positions −96 and −21 are indicated by asterisks.