Shan B, Zhu X, Chen P L, Durfee T, Yang Y, Sharp D, Lee W H
Center for Molecular Medicine/Institute of Biotechnology, University of Texas Health Science Center, San Antonio 78245.
Mol Cell Biol. 1992 Dec;12(12):5620-31. doi: 10.1128/mcb.12.12.5620-5631.1992.
The retinoblastoma protein interacts with a number of cellular proteins to form complexes which are probably crucial for its normal physiological function. To identify these proteins, we isolated nine distinct clones by direct screening of cDNA expression libraries using purified RB protein as a probe. One of these clones, Ap12, is expressed predominantly at the G1-S boundary and in the S phase of the cell cycle. The nucleotide sequence of Ap12 has features characteristic of transcription factors. The C-terminal region binds to unphosphorylated RB in regions similar to those to which T antigen binds and contains a transactivation domain. A region containing a potential leucine zipper flanked by basic residues is able to bind an E2F recognition sequence specifically. Expression of Ap12 in mammalian cells significantly enhances E2F-dependent transcriptional activity. These results suggest that Ap12 encodes a protein with properties known to be characteristic of transcription factor E2F.
视网膜母细胞瘤蛋白与许多细胞蛋白相互作用形成复合物，这些复合物可能对其正常生理功能至关重要。为了鉴定这些蛋白，我们以纯化的RB蛋白为探针，通过直接筛选cDNA表达文库分离出了9个不同的克隆。其中一个克隆Ap12主要在细胞周期的G1-S边界和S期表达。Ap12的核苷酸序列具有转录因子的特征。其C末端区域在与T抗原结合的相似区域与未磷酸化的RB结合，并包含一个反式激活结构域。一个含有潜在亮氨酸拉链且两侧为碱性残基的区域能够特异性结合E2F识别序列。Ap12在哺乳动物细胞中的表达显著增强了E2F依赖的转录活性。这些结果表明，Ap12编码一种具有已知转录因子E2F特征的蛋白。
