Transportin 1 is the beta subunit of the karyopherin receptor complex which interacts with nuclear localization signals to target proteins to the nucleus. The karyopherin receptor complex is a heterodimer of an alpha subunit which recognizes the nuclear localization signal and a beta subunit which docks the complex at nucleoporins. Alternate splicing of this gene results in two transcript variants encoding different proteins. In cases of HIV-1 infections, transportin 1 is known to bind and mediate the nuclear import of HIV-1 Rev.