Lt. Lam et Eh. Bresnick, EVIDENCE FOR DISTINCT DNA-BINDING FORMS OF THE ERYTHROID-SPECIFIC TRANSCRIPTION FACTOR NF-E2, Biochemistry, 34(50), 1995, pp. 16347-16358
The transcriptional activity of the beta-globin genes is regulated by
a complex genetic element, the locus control region (LCR), at the 5'-e
nd of the beta-globin locus. Tandem binding sites for the erythroid-sp
ecific transcription factor NF-E2 are important for the transcriptiona
l activation function of the LCR. We discovered that vanadate strongly
stimulates the DNA binding activity of NF-E2 in crude and fractionate
d nuclear extracts. The other oxyanions, molybdate and tungstate, do n
ot affect NF-E2 DNA binding. Quantitative DNA binding experiments indi
cated that vanadate stimulates NF-E2 DNA binding by increasing the num
ber of NF-E2 molecules that are competent to bind to DNA, rather than
influencing the affinity of binding. Gel filtration analysis revealed
a similar Stokes' radius for NF-E2, in the absence or presence of vana
date, inconsistent with a role for vanadate in stabilizing the heterom
eric NF-E2 complex. Distinct NF-E2 forms, which were either weakly or
strongly induced by vanadate, were resolved by cation and anion exchan
ge chromatography. A model is proposed in which two conformers of NF-E
2 share an identical subunit composition, but differ in DNA binding ac
tivity. Vanadate may interact directly with one of the conformers to g
enerate the high-affinity DNA binding state. The presence of a non-DNA
binding pool of NF-E2 suggests that the formation of an active NF-E2
heteromer may be a regulated step in the cell.