Jones K A, Tjian R
Cell. 1984 Jan;36(1):155-62. doi: 10.1016/0092-8674(84)90084-9.
Essential nucleotide contacts between the SV40 large T (tumor) antigen and binding sites I and II on the SV40 genome have been inferred from in vitro methylation- and ethylation-interference experiments. Each site contains two clusters of guanine residues that reduce the specific binding of T antigen when modified. Methylation at any one of nine guanines within site I or any one of five guanines within site II severely interferes with the interaction of T antigen with each respective site. Methylation at any one of a second group of five guanines within site II results in an appreciably weaker effect on the binding of T antigen. A similar inhibitory effect on binding is observed upon ethylation of adjacent phosphate residues. Although there are significant differences in the nucleotide sequence of the two binding sites, the pattern of protein contacts is strikingly similar between sites I and II. Three-dimensional projection reveals that the guanine contacts within each binding site are localized so that the specific binding interactions are accessible from only one face of the DNA helix.
通过体外甲基化和乙基化干扰实验，已推断出猴病毒40型（SV40）大T（肿瘤）抗原与SV40基因组上的结合位点I和II之间的必需核苷酸接触。每个位点包含两簇鸟嘌呤残基，修饰后会降低T抗原的特异性结合。位点I内九个鸟嘌呤中的任何一个甲基化或位点II内五个鸟嘌呤中的任何一个甲基化都会严重干扰T抗原与各自位点的相互作用。位点II内第二组五个鸟嘌呤中的任何一个甲基化对T抗原结合的影响明显较弱。相邻磷酸残基乙基化时，对结合也观察到类似的抑制作用。尽管两个结合位点的核苷酸序列存在显著差异，但位点I和II之间的蛋白质接触模式非常相似。三维投影显示，每个结合位点内的鸟嘌呤接触是定位的，因此特异性结合相互作用仅可从DNA螺旋的一个面接近。
