Zhao L J, Padmanabhan R
Department of Biochemistry and Molecular Biology, University of Kansas Medical Center, Kansas City 66103.
Cell. 1988 Dec 23;55(6):1005-15. doi: 10.1016/0092-8674(88)90245-0.
The mRNAs for the 80 kd adenovirus preterminal protein (pTP) and the 140 kd DNA polymerase (AdPol) contain several exons spliced to the main open reading frames (m-ORFs) located in the early transcription unit E2B. These proteins were transiently expressed in monkey kidney cells (CV1) utilizing the first ATG (pTP1 and AdPol1) or the ATG of a linker inserted at the beginning of the m-ORFs (pTP2 and AdPol2). Only pTP2 and AdPol2 were functionally active in an in vitro replication initiation assay. Both pTP1 and pTP2 were transported to the nucleus. The sequence RLPV(R)6VP, which is present in both pTPs, is identified as their nuclear localization signal. In contrast, AdPol1 was cytoplasmically localized, whereas AdPol2 was distributed in both compartments, suggesting that the nuclear localization signal for AdPol is within the first 139 amino acids. Interestingly, when AdPol1 and pTP1 or AdPol2 and pTP2 were coexpressed in the transfected cells, the nuclear distribution of AdPol1 or AdPol2 was significantly increased. We demonstrate that the nuclear transport of AdPol is facilitated, irrespective of the presence of its nuclear localization signal, by interaction with pTP.
80kd腺病毒前末端蛋白（pTP）和140kd DNA聚合酶（AdPol）的信使核糖核酸（mRNA）包含几个外显子，这些外显子剪接到位于早期转录单元E2B中的主要开放阅读框（m-ORF）上。利用第一个甲硫氨酸（pTP1和AdPol1）或插入到m-ORF起始处的接头的甲硫氨酸（pTP2和AdPol2），这些蛋白质在猴肾细胞（CV1）中瞬时表达。在体外复制起始试验中，只有pTP2和AdPol2具有功能活性。pTP1和pTP2都被转运到细胞核。两种pTP中都存在的序列RLPV(R)6VP被确定为它们的核定位信号。相比之下，AdPol1定位于细胞质，而AdPol2分布在两个区室中，这表明AdPol的核定位信号在最初的139个氨基酸内。有趣的是，当AdPol1和pTP1或AdPol2和pTP2在转染细胞中共表达时，AdPol1或AdPol2的核分布显著增加。我们证明，通过与pTP相互作用，AdPol的核转运得到促进，而与其核定位信号的存在无关。
