Cut/CDP binding activity is undetectable in human primary monocytes/macrophages. (A) Nuclear cell extracts from freshly isolated monocytes and fully differentiated macrophages were incubated with CDP-labeled oligonucleotide derived from the gp91-phox promoter and analyzed by EMSA. Nuclear cell extracts were from HeLa cells and U937 cells undifferentiated or induced to monocyte differentiation with 125OH-vitamin D₃ for 2, 3, and 4 days. (B) The same nuclear extracts were incubated with a labeled specific consensus Cut binding site.27 (C) Whole (lane 1) and nuclear cell (lane 4) extracts prepared from freshly isolated monocytes were incubated with a labeled PU.1 oligonucleotide to test extract integrity. Competition assay with wild-type (lane 2) and mutated oligonucleotide (lane 3) was also performed on whole cell extracts.