TNPO3 is a member of the importin beta/transportin family of nuclear import receptors and is specific for the essential splicing factors termed SR proteins, binding specifically and directly to the arginine/serine (RS)-rich domains of these proteins. Further experiments demonstrated that this interaction occurs only when these RS domains are phosphorylated. More recently, TNPO3 was identified as an HIV dependency factor (HDF) and that depletion of TNPO3 resulted in HIV inhibition after reverse transcription but before integration, suggesting that TNPO3 may be an important drug target in HIV treatment. At least three isoforms of TNPO3 are known to exist.