Kaneko H, Orii K O, Matsui E, Shimozawa N, Fukao T, Matsumoto T, Shimamoto A, Furuichi Y, Hayakawa S, Kasahara K, Kondo N
Department of Pediatrics, Gifu University School of Medicine, Japan.
Biochem Biophys Res Commun. 1997 Nov 17;240(2):348-53. doi: 10.1006/bbrc.1997.7648.
Bloom syndrome (BS) is a rare genetic disorder characterized by small body size, sun sensitivity, immunodeficiency and a high predisposition to various types of cancer. BLM was identified as the causative gene for BS, and BLM protein is homologous to DNA helicase. There are two putative nuclear localization signals (NLSs) within amino acid residues 1334-1349 in the C-terminus of the BLM protein, which has the distinctive structure of two basic residue arms separated by a spacer. The entire coding or deleted BLM sequences of various sizes were ligated into an enhanced green fluorescent protein (EGFP) vector and transfected into HeLa cells. The EGFP vector harboring the entire BLM coding sequence was transported to the nucleus. The BLM protein truncated at 1341 amino acid, containing an intact helicase domain and only one proximal arm, was not transported to the nucleus. The BLM protein truncated at 1357 amino acid, containing an intact helicase domain and two arms, was transported to the nucleus. The EGFP vector harboring DNA fragments encoding a protein having only the distal arms of basic amino acids in the C-terminus was also transported to the nucleus. The truncated BLM proteins corresponding to previously reported mutated BLM proteins were retained in the cytoplasm or both the cytoplasm and the nucleus as was the EGFP vector with no insert. These results show that the BLM protein translocates into the nucleus and that the distal arm of the bipartite basic residues in the C-terminus of the BLM protein is essential for targeting the nucleus.
布卢姆综合征（BS）是一种罕见的遗传性疾病，其特征为身材矮小、对阳光敏感、免疫缺陷以及极易患各种类型的癌症。BLM被确定为BS的致病基因，且BLM蛋白与DNA解旋酶同源。在BLM蛋白C端的1334 - 1349氨基酸残基内有两个推定的核定位信号（NLSs），其具有由一个间隔区隔开的两个碱性残基臂的独特结构。将各种大小的完整编码或缺失的BLM序列连接到增强型绿色荧光蛋白（EGFP）载体中，并转染到HeLa细胞中。携带完整BLM编码序列的EGFP载体被转运到细胞核。在第1341个氨基酸处截断的BLM蛋白，包含一个完整的解旋酶结构域且只有一个近端臂，未被转运到细胞核。在第1357个氨基酸处截断的BLM蛋白，包含一个完整的解旋酶结构域和两个臂，被转运到细胞核。携带编码仅在C端具有碱性氨基酸远端臂的蛋白质的DNA片段的EGFP载体也被转运到细胞核。与先前报道的突变BLM蛋白相对应的截断型BLM蛋白保留在细胞质中，或同时存在于细胞质和细胞核中，没有插入片段的EGFP载体也是如此。这些结果表明BLM蛋白易位进入细胞核，并且BLM蛋白C端二分碱性残基的远端臂对于靶向细胞核至关重要。
