Nucleus-specific importin alpha proteins and nucleoporins regulate protein import and nuclear division in the binucleate Tetrahymena thermophila

Eukaryot Cell. 2008 Sep;7(9):1487-99. doi: 10.1128/EC.00193-08. Epub 2008 Aug 1.


The ciliate Tetrahymena thermophila, having both germ line micronuclei and somatic macronuclei, must possess a specialized nucleocytoplasmic transport system to import proteins into the correct nucleus. To understand how Tetrahymena can target proteins to distinct nuclei, we first characterized FG repeat-containing nucleoporins and found that micro- and macronuclei utilize unique subsets of these proteins. This finding implicates these proteins in the differential permeability of the two nuclei and implies that nuclear pores with discrete specificities are assembled within a single cell. To identify the import machineries that interact with these different pores, we characterized the large families of karyopherin homologs encoded within the genome. Localization studies of 13 putative importin (imp) alpha- and 11 imp beta-like proteins revealed that imp alpha-like proteins are nucleus specific--nine localized to the germ line micronucleus--but that most imp beta-like proteins localized to both types of nuclei. These data suggest that micronucleus-specific proteins are transported by specific imp alpha adapters. The different imp alpha proteins exhibit substantial sequence divergence and do not appear to be simply redundant in function. Disruption of the IMA10 gene encoding an imp alpha-like protein that accumulates in dividing micronuclei results in nuclear division defects and lethality. Thus, nucleus-specific protein import and nuclear function in Tetrahymena are regulated by diverse, specialized karyopherins.

Publication types

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

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Cell Nucleus / chemistry
  • Cell Nucleus / genetics
  • Cell Nucleus / metabolism*
  • Cell Nucleus Division*
  • Macronucleus / genetics
  • Macronucleus / metabolism
  • Molecular Sequence Data
  • Nuclear Pore Complex Proteins / chemistry
  • Nuclear Pore Complex Proteins / genetics
  • Nuclear Pore Complex Proteins / metabolism*
  • Protein Structure, Tertiary
  • Protein Transport
  • Protozoan Proteins / chemistry
  • Protozoan Proteins / genetics
  • Protozoan Proteins / metabolism*
  • Sequence Alignment
  • Tetrahymena thermophila / chemistry
  • Tetrahymena thermophila / cytology*
  • Tetrahymena thermophila / genetics
  • Tetrahymena thermophila / metabolism*
  • alpha Karyopherins / chemistry
  • alpha Karyopherins / genetics
  • alpha Karyopherins / metabolism*


  • Nuclear Pore Complex Proteins
  • Protozoan Proteins
  • alpha Karyopherins