Purification and characterization of ATBP, a novel protein that binds to A/T stretches in three segments of the Sarcophaga lectin gene

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Abstract
A DNA‐binding protein for the Sarcophaga lectin gene, ATBP (A/T‐stretches‐binding protein) was purified to homogeneity from the nuclear extract of NIH‐Sape‐4 cells. The molecular mass of ATBP determined under denaturing conditions was 53 kDa, but its native molecular mass estimated by gel‐filtration chromatography was 430 kDa, suggesting that it is an octamer of the 53‐kDa subunit. This protein bound to at least three DNA fragments from the Sarcophaga lectin gene, two of them are in the 5′‐upstream region and the other is in a region containing an intron. These fragments are very AT rich and inlaid with stretches of A or T residues (A/T stretches). ATBP was found to have affinity for poly[d(A‐T)]. These results suggest that ATBP binds to A/T stretches in the three DNA fragments from this gene. Furthermore, longer DNA was found to be bound more effectively, suggesting that an octamer of the 53‐kDa subunit has multiple binding sites for the DNA fragments and requires a relatively long DNA sequence for binding.