HAF-1 and PU.1 complexes increase in intensity after overexpression of Elf-1 or PU.1. EMSA was performed as described in Materials and Methods. Probe corresponding to the −68 to −30 bp region of the gp91^phox promoter was incubated with 8 μg of total cellular protein isolated from K562 cells 15 hours after electroporation with Elf-1 or PU.1 expression vectors. K562 cells were transfected similarly to that described in Materials and Methods for PLB985 cells. The lane containing nuclear extract isolated from PLB985 cells provides a standard for the mobilities of the HAF-1 and PU.1 complexes. Antisera and blocking peptides were added where indicated. The relative intensity of EMSA complexes produced by whole cell protein extracts cannot be directly compared with that produced by the nuclear extract.