Proteins involved in the import of ribonucleoproteins into the nucleus. Transportin-1 (TNPO1, karyopherin β2, 898 aa) and TNPO2 (karyopherin β2B, importin β2, 897 aa) have different binding specificities for pre-mRNA/mRNA-binding proteins (heterogeneous nuclear ribonucleoproteins, hnRNP) that have an M9 domain. Transportin-SR (transportin-3, 923 aa), binds the phosphorylated RS domains of various proteins and is responsible for targeting SR-proteins to the nucleus. Activity is regulated by Ran-GTP. See importins.
Subjects: Medicine and Health.