Masutani C, Kusumoto R, Yamada A, Dohmae N, Yokoi M, Yuasa M, Araki M, Iwai S, Takio K, Hanaoka F
Institute for Molecular and Cellular Biology, Osaka University, Suita, Japan.
Nature. 1999 Jun 17;399(6737):700-4. doi: 10.1038/21447.
Xeroderma pigmentosum variant (XP-V) is an inherited disorder which is associated with increased incidence of sunlight-induced skin cancers. Unlike other xeroderma pigmentosum cells (belonging to groups XP-A to XP-G), XP-V cells carry out normal nucleotide-excision repair processes but are defective in their replication of ultraviolet-damaged DNA. It has been suspected for some time that the XPV gene encodes a protein that is involved in trans-lesion DNA synthesis, but the gene product has never been isolated. Using an improved cell-free assay for trans-lesion DNA synthesis, we have recently isolated a DNA polymerase from HeLa cells that continues replication on damaged DNA by bypassing ultraviolet-induced thymine dimers in XP-V cell extracts. Here we show that this polymerase is a human homologue of the yeast Rad30 protein, recently identified as DNA polymerase eta. This polymerase and yeast Rad30 are members of a family of damage-bypass replication proteins which comprises the Escherichia coli proteins UmuC and DinB and the yeast Rev1 protein. We found that all XP-V cells examined carry mutations in their DNA polymerase eta gene. Recombinant human DNA polymerase eta corrects the inability of XP-V cell extracts to carry out DNA replication by bypassing thymine dimers on damaged DNA. Together, these results indicate that DNA polymerase eta could be the XPV gene product.
着色性干皮病变异型（XP-V）是一种遗传性疾病，与阳光诱发的皮肤癌发病率增加有关。与其他着色性干皮病细胞（属于XP-A至XP-G组）不同，XP-V细胞能进行正常的核苷酸切除修复过程，但在复制紫外线损伤的DNA时存在缺陷。一段时间以来，人们一直怀疑XPV基因编码一种参与跨损伤DNA合成的蛋白质，但该基因产物从未被分离出来。我们最近使用一种改进的无细胞跨损伤DNA合成检测方法，从HeLa细胞中分离出一种DNA聚合酶，它在XP-V细胞提取物中通过绕过紫外线诱导的胸腺嘧啶二聚体，在损伤的DNA上继续复制。在此我们表明，这种聚合酶是酵母Rad30蛋白的人类同源物，最近被鉴定为DNA聚合酶η。这种聚合酶和酵母Rad30是一类损伤绕过复制蛋白家族的成员，该家族包括大肠杆菌蛋白UmuC和DinB以及酵母Rev1蛋白。我们发现，所有检测的XP-V细胞在其DNA聚合酶η基因中都携带突变。重组人DNA聚合酶η通过绕过损伤DNA上的胸腺嘧啶二聚体，纠正了XP-V细胞提取物进行DNA复制的无能。这些结果共同表明，DNA聚合酶η可能是XPV基因产物。
