TNPO3

TNPO3 is a nuclear import receptor for serine/arginine-rich (SR) proteins such as the splicing factors SFRS1 and SFRS2. TNPO3 has also been shown to be involved in HIV-1 infection, apparently through interaction with the HIV-1 capsid protein.

Full Name

Transportin 3

Function

Importin, which transports target proteins into the nucleus (PubMed:10366588, PubMed:10713112, PubMed:11517331, PubMed:12628928, PubMed:24449914).
Specifically mediates the nuclear import of splicing factor serine/arginine (SR) proteins, such as RBM4, SFRS1 and SFRS2, by recognizing phosphorylated SR domains (PubMed:10366588, PubMed:10713112, PubMed:11517331, PubMed:12628928, PubMed:24449914).
Also mediates the nuclear import of serine/arginine (SR) protein CPSF6, independently of CPSF6 phosphorylation (PubMed:30916345, PubMed:31465518).
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 (PubMed:23878195, PubMed:24449914).
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 (PubMed:23878195, PubMed:24449914).
(Microbial infection) Involved in immunodeficiency virus (HIV-1) infection by importing the pre-integration complex (PIC) into the nucleus (PubMed:18722123, PubMed:21901095, PubMed:22398280, PubMed:29329553).
Required for a nuclear maturation step of HIV-1 prior to integration (PubMed:21901095, PubMed:22398280).

Biological Process

Protein import into nucleus

Cellular Location

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.

Involvement in disease

Muscular dystrophy, limb-girdle, autosomal dominant 2 (LGMDD2):
An autosomal dominant myopathy characterized by proximal muscle weakness primarily affecting the lower limbs, but also affecting the upper limbs in most patients. Affected individuals also have distal muscle weakness of the hands and lower leg muscles. The disease has generally a benign clinical course but some individuals with childhood or juvenile onset manifest severe widespread myopathy, leading to wheelchair dependency and respiratory insufficiency. Muscle biopsy shows dystrophic changes with abnormal nuclei, rimmed vacuoles, and filamentous inclusions.