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

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.