Interaction of Sp1 with the β₃ promoter. EMSA using ³²P-labeled mMS7 or MS7 oligonucleotide probes incubated with K562 nuclear protein or purified Sp1 protein as indicated above by the “+.” Sp1-purified protein was used at 1.5 μg/sample. Lanes 7 through 10 are from a different gel that was run longer. The appearance of the 7b band was inconsistently observed with purified Sp1 and this probe. Anti-Sp1 antibody or the irrelevant mouse Ig (irrel. Ab) was added to samples as indicated by the “+” above. Prefix “m” indicates mutant oligonucleotide, as described in Table 1.