Miller Kristi A, Hinz John M, Yamada N Alice, Thompson Lawrence H, Albala Joanna S
Biology and Biotechnology Research Program, Lawrence Livermore National Laboratory, 7000 East Avenue, L-448, Livermore, CA 94550, USA.
Mutagenesis. 2005 Jan;20(1):57-63. doi: 10.1093/mutage/gei011. Epub 2005 Feb 8.
Rad51B is one of the five paralogs of human Rad51 and is found in a multiprotein complex with three other Rad51 paralogs, Rad51C, Rad51D and Xrcc2. Participation of Rad51B in this complex depends on its direct interaction with Rad51C. Examination of EGFP-Rad51B fusion protein in HeLa S3 cells and immunofluorescence in several human cell lines reveal the nuclear localization of Rad51B. Mutations in the N-terminal KKLK motif of Rad51B (amino acids 4-7), result in the cytoplasmic localization of Rad51B suggesting that the KKLK sequence is the nuclear localization signal (NLS) for the Rad51B protein. Examination of wild-type EGFP-Rad51B fusion protein in hamster irs3 mutant cells, deficient in Rad51C, showed that Rad51B localizes to the nucleus independently of Rad51C, the only known direct binding partner for Rad51B. Utilization of a BRCA2 mutant cell line, CAPAN-1, showed that Rad51B also localizes to the nucleus independent of BRCA2. Although both Rad51B and BRCA2 are clearly involved in the homologous recombinational repair pathway, Rad51B and BRCA2 do not appear to associate. This study finds that a KKLK motif in the N-terminus of Rad51B serves as an NLS that allows Rad51B to localize to the nucleus independent of Rad51C or BRCA2.
Rad51B是人类Rad51五个旁系同源物之一，它与其他三个Rad51旁系同源物Rad51C、Rad51D和Xrcc2存在于一个多蛋白复合物中。Rad51B参与该复合物依赖于它与Rad51C的直接相互作用。对HeLa S3细胞中EGFP-Rad51B融合蛋白的检测以及在几种人类细胞系中的免疫荧光检测揭示了Rad51B的核定位。Rad51B的N端KKLK基序（氨基酸4-7）发生突变会导致Rad51B定位于细胞质，这表明KKLK序列是Rad51B蛋白的核定位信号（NLS）。在缺乏Rad51C的仓鼠irs3突变细胞中检测野生型EGFP-Rad51B融合蛋白，结果表明Rad51B独立于Rad51C定位于细胞核，Rad51C是Rad51B唯一已知的直接结合伴侣。利用BRCA2突变细胞系CAPAN-1进行研究表明，Rad51B也独立于BRCA2定位于细胞核。尽管Rad51B和BRCA2都明显参与同源重组修复途径，但Rad51B和BRCA2似乎并不相互关联。本研究发现，Rad51B N端的KKLK基序作为一个核定位信号，使Rad51B能够独立于Rad51C或BRCA2定位于细胞核。
