Analysis of transcription factors GATA-1 and SP1 in CBL culture, second phase
(a) Autoradiogram of gel retardation assay. The numbers on top represent days in the second phase, after EPO addition. K562, an erythroleukemia cell line serving as a positive control; competition, binding in the presence of 100-fold molar excess of unlabeled competitor oligonucleotide. The lower band in the SP1 retardation assay, which comigrates with the GATA-1-shifted band, is probably due to nonspecific binding (17). (b) Quantitative analysis of the autoradiograms. ●, GATA-1 binding activity; ○, SP1 binding activity.