Two binding sites for the G1/G2 complexes. (A) Binding of G1/G2 to FP8. The binding assay was done under standard conditions, using a HeLa extract. Competitor DNA (100 ng) was added as indicated above the lanes. 0, no competitor; G, GALCAT competitor (see Table 1); this competitor binds the G1/G2 complexes³⁷; 13 and 14, human FP probes. (B) Competition assay to define the complexes that bind probe FP13. K562 extracts were used. The identities of the complexes, established by these and other competition and binding assays are indicated at left. Competitors (100 ng) added were: 0, no competitor; S, FP13; 8, FP8; G, GALCAT; γ-175, from the human γ promoter −175 region (see Table 1), an oligonucleotide that binds GATA-1, GATA-like proteins and Oct-1.32,33 Although the GATA complex bound by FP13 comigrates with GATA-1, it is not erythroid specific (data not shown). A similar complex (called NOTAGATA) has been noted in HS2 (Zhu et al, unpublished data). (C) Cell-type specificity of the factors that bind to FP13. The G1/G2 complexes are not found in Jurkat cells (J) as indicated earlier,37 but are present in other nonerythroid cells (not shown). Likewise, complex (5) is missing in Jurkat cells, and present in K562 cells (K) as well as several other cell types (CaCo2 and HeLa cells, data not shown).