Mapping of the regions implicated in nuclear localization of multi-functional DNA repair endonuclease XPF-ERCC1

The structure-specific endonuclease XPF-ERCC1 is a multi-functional heterodimer that participates in a variety of DNA repair mechanisms for maintaining genome integrity. Both subunits contain C-terminal tandem helix-hairpin-helix (HhH(2)) domains, which are necessary for not only their dimerization but also enzymatic activity as well as protein stability. However, the interdependency of both subunits in their nuclear localization remains poorly understood. In this study, we have analyzed the region(s) that affects the subcellular localization of XPF and ERCC1 using various deletion mutants. We first identified the nuclear localization signal (NLS) in XPF, which was essential for its nuclear localization under the ERCC1-free condition, but dispensable in the presence of ERCC1 (probably as XPF-ERCC1 heterodimer). Interestingly, in the NLS-independent and ERCC1-dependent XPF nuclear localization, the physical interaction between XPF and ERCC1 via C-terminal HhH(2) domains was not needed. Instead, the amino acid regions 311-469 of XPF and 216-260 of ERCC1 are required for the nuclear localization. Furthermore, we found that the 311-469 region of XPF interacts with ERCC1 in a co-immunoprecipitation assay. These results suggest that the nuclear localization of XPF-ERCC1 heterodimer is regulated at multiple levels in an interdependent manner.

Automated summary

This study analyzed the regions that affect the subcellular localization of XPF and ERCC1 and found that the nuclear localization of XPF is dependent on ERCC1 and regulated at multiple levels. The nuclear localization signal (NLS) in XPF is essential for its nuclear localization in the absence of ERCC1, but dispensable in the presence of ERCC1. The amino acid regions 311-469 of XPF and 216-260 of ERCC1 are required for the nuclear localization and the physical interaction between XPF and ERCC1 via C-terminal HhH(2) domains is not needed in the ERCC1-dependent XPF nuclear localization.