A DISTINCT NUCLEAR IMPORT PATHWAY USED BY RIBOSOMAL-PROTEINS

Protein transport into the nucleus is governed by the interaction of s oluble transport factors with their import substrates and nuclear pore complexes. Here, we identify a major distinct nuclear import pathway, mediated by a previously uncharacterized yeast beta karyopherin Kap12 3p. The predominant substrates for this pathway are ribosomal proteins , which must be imported into the nucleus prior to assembly into pre-r ibosomes. Kap123p binds directly to its transport substrates, repeat m otif-containing nucleoporins, and Ran-GTP. We show that the related pr otein Pse1p is also a karyopherin and can functionally substitute for Kap123p; both are capable of specifically directing a ribosomal nuclea r localization signal reporter to the nucleus in vivo.