Probable ubiquitin ligase protein involved in mRNA export. E3 ubiquitin ligase proteins mediate ubiquitination and subsequent proteasomal degradation of target proteins. Probably participates in mRNA export from the nucleus by regulating the transport of hnRNP proteins such as rae1. S-ubiquitinyl-[E2 ubiquitin-conjugating enzyme]-L-cysteine + [acceptor protein]-L-lysine = [E2 ubiquitin-conjugating enzyme]-L-cysteine + N(6)-ubiquitinyl-[acceptor protein]-L-lysine. Protein modification; protein ubiquitination. Belongs to the UPL family. TOM1/PTR1 subfamily.