Transportin 1: Proteins and Enzymes

Heterogeneous nuclear ribonucleoprotein hnRNPA1 is an abundant nuclear protein that plays an important role in pre-mRNA processing and mRNA export from the nucleus. A1 shuttles rapidly between the nucleus and the cytoplasm, and a 38-amino acid domain, M9, serves as the bi-directional transport signal of A1. Recently, a 90-kD protein, transportin, was identified as the mediator of A1 nuclear import. Transportin mediates the nuclear import of additional hnRNP proteins, including hnRNPF. The nuclear localization of A1 is dependent on ongoing RNA polymerase II transcription.