Importin, which transports target proteins into the nucleus (  ). Specifically mediates the nuclear import of splicing factor serine/arginine (SR) proteins, such as RBM4, SFRS1 and SFRS2, by recognizing phosphorylated SR domains (  ). Also mediates the nuclear import of serine/arginine (SR) protein CPSF6, independently of CPSF6 phosphorylation (, ). The nuclear import process is regulated by the small GTPase Ran that partitions between cytoplasm and nucleus in the predominantly GDP- and GTP-bound form, respectively (, ). Importin associates with target cargo proteins in the cytoplasm, and the competitive binding of GTP-bound Ran induces the release of cargos in the nucleus (, ).
(Microbial infection) Involved in immunodeficiency virus (HIV-1) infection by importing the pre-integration complex (PIC) into the nucleus ( , ). Required for a nuclear maturation step of HIV-1 prior to integration (, ).
Subcellular locations: Nucleus envelope, Cytoplasm
Localizes to the nuclear envelope and annulate lamellae, which consists in stacks of endoplasmic reticulum membranes containing a high density of nuclear pores.
Expressed in skeletal muscle.