APOBEC3B Nuclear Localization Requires Two Distinct N-Terminal Domain Surfaces

J Mol Biol. 2018 Aug 17;430(17):2695-2708. doi: 10.1016/j.jmb.2018.04.044. Epub 2018 May 19.


The APOBEC3 family of cytosine deaminases catalyzes the conversion of cytosines-to-uracils in single-stranded DNA. Traditionally, these enzymes are associated with antiviral immunity and restriction of DNA-based pathogens. However, a role for these enzymes in tumor evolution and metastatic disease has also become evident. The primary APOBEC3 candidate in cancer mutagenesis is APOBEC3B (A3B) for three reasons: (1) A3B mRNA is upregulated in several different cancers, (2) A3B expression and mutational loads correlate with poor clinical outcomes, and (3) A3B is the only family member known to be constitutively nuclear. Previous studies have mapped non-canonical A3B nuclear localization determinants to a single surface-exposed patch within the N-terminal domain (NTD). Here, we show that A3B has an additional, distinct, surface-exposed NTD region that contributes to nuclear localization. Disruption of residues within the first 30 amino acids of A3B (import surface 1) or loop 5/α-helix 3 (import surface 2) completely abolish nuclear localization. These import determinants also graft into NTDs of related family members and mediate re-localization from cell-wide-to-nucleus or cytoplasm-to-nucleus. These findings demonstrate that both sets of residues are required for non-canonical A3B nuclear localization and describe unique surfaces that may serve as novel therapeutic targets.

Keywords: APOBEC3B; cancer genomic DNA deaminase; nuclear import; retrovirus restriction factor; subcellular localization.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Amino Acid Substitution
  • Cell Nucleus / genetics
  • Cell Nucleus / metabolism*
  • Cytidine Deaminase / chemistry*
  • Cytidine Deaminase / genetics
  • Cytidine Deaminase / metabolism*
  • HEK293 Cells
  • HeLa Cells
  • Humans
  • Minor Histocompatibility Antigens / chemistry*
  • Minor Histocompatibility Antigens / genetics
  • Minor Histocompatibility Antigens / metabolism*
  • Mutation
  • Nuclear Localization Signals / genetics*
  • Protein Conformation
  • Protein Domains
  • Sequence Homology


  • Minor Histocompatibility Antigens
  • Nuclear Localization Signals
  • APOBEC3B protein, human
  • Cytidine Deaminase