Figure 4

Sequential molecular interactions in the A2 pathway. Molecular interactions associated with sequential steps in the A2 pathway are illustrated. In the first step, newly synthesized hnRNP A2 binds to transportin in the cytoplasm and is imported into the nucleus. In the nucleus, transportin binds either RanGTP or hnRNP A2 and hnRNP A2 binds either A2RE RNA or tansportin. In the next step, hnRNP A2 oligomers bind to A2RE RNA in the nucleus and are exported to the cytoplasm. In the cytoplasm, hnRNP A2 dimers bind either to other hnRNP A2 dimers or to TOG protein, which mediates granule assembly. In the next step, hnRNP A2 binds both TOG protein and hnRNP E1, which inhibits translation during transport. In the last step, granules bind either hnRNP E1 or ribosomal subunits, to initiate translation. Steps involving either or interactions are essentially irreversible and promote polarity to the pathway. Steps involving both and interactions are reversible.