Fig. 1. Comparison of amino acid conservation and DNA-binding properties of Pho and Pho-like. (A) Amino acid identity (boxed) between Pho and Phol over the four zinc fingers. Amino acids from human YY1 that have been shown by X-ray crystallography to interact with DNA are marked (Houbaviy et al., 1996). Black circles represent amino acids that contact the DNA backbone. (+) represents positions that contact the DNA bases. White circles represent amino acids that contact both the DNA backbone and the bases. Cys and His residues of the zinc fingers are in bold. (B) Amino acid conservation within the spacer region between Pho, Phol and human YY1 (hYY1). Bold type indicates amino acids that are conserved between all three proteins. (C) The DNA sequence of the Pho and mutated Pho-binding site oligonucleotides used to test the DNA-binding specificity of the Phol zinc fingers. The mutated bases are denoted by the arrows. The Pho binding site is boxed. (D) Autoradiogram of a gel mobility shift assay showing binding of full-length Pho (lanes 1-3) and Phol zinc-finger protein (lanes 4-6) to the Pho-binding site. Lanes 1 and 4, no competitor DNA; lanes 2 and 5, 100x unlabeled Pho-binding site; lanes 3 and 6, 100x unlabeled mutated Pho-binding site. The specific Pho and Phol complexes are indicated by arrowheads. The broken arrow denotes a faint gel shift due to endogenous YY1 protein in the reticulocyte lysate.