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Open Access Research article

Karyopherin α7 (KPNA7), a divergent member of the importin α family of nuclear import receptors

Joshua B Kelley1, Ashley M Talley1, Adam Spencer1, Daniel Gioeli2 and Bryce M Paschal13*

Author affiliations

1 Center for Cell Signaling, University of Virginia, Charlottesville, VA, 22908, USA

2 Department of Microbiology, University of Virginia, Charlottesville, VA, 22908, USA

3 Department of Biochemistry and Molecular Genetics, University of Virginia, Charlottesville, VA, 22908, USA

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Citation and License

BMC Cell Biology 2010, 11:63  doi:10.1186/1471-2121-11-63

Published: 11 August 2010

Abstract

Background

Classical nuclear localization signal (NLS) dependent nuclear import is carried out by a heterodimer of importin α and importin β. NLS cargo is recognized by importin α, which is bound by importin β. Importin β mediates translocation of the complex through the central channel of the nuclear pore, and upon reaching the nucleus, RanGTP binding to importin β triggers disassembly of the complex. To date, six importin α family members, encoded by separate genes, have been described in humans.

Results

We sequenced and characterized a seventh member of the importin α family of transport factors, karyopherin α 7 (KPNA7), which is most closely related to KPNA2. The domain of KPNA7 that binds Importin β (IBB) is divergent, and shows stronger binding to importin β than the IBB domains from of other importin α family members. With regard to NLS recognition, KPNA7 binds to the retinoblastoma (RB) NLS to a similar degree as KPNA2, but it fails to bind the SV40-NLS and the human nucleoplasmin (NPM) NLS. KPNA7 shows a predominantly nuclear distribution under steady state conditions, which contrasts with KPNA2 which is primarily cytoplasmic.

Conclusion

KPNA7 is a novel importin α family member in humans that belongs to the importin α2 subfamily. KPNA7 shows different subcellular localization and NLS binding characteristics compared to other members of the importin α family. These properties suggest that KPNA7 could be specialized for interactions with select NLS-containing proteins, potentially impacting developmental regulation.