Origins and division of labor in trypanosome RNA processing through expanded Mex67 paralogs

In contrast to most nucleocytoplasmic transport, canonical mRNA export requires ATP-dependent remodeling machinery and is Ran-independent. Remarkably, we show here that trypanosomes have three distinct Mex67 paralogs that we term TbMex67, TbMex67b and TbMex67L.

Each has a distinct non-redundant role in rRNA processing and mRNA export. Specifically, TbMex67 and TbMex67b retain roles in mRNA export, albeit associating with specific mRNA cohorts and differing protein and mRNA interactomes in vertebrate and procyclic (insect) form parasites. Further, TbMex67 and TbMex67b paralogs associate with the Ran export machinery, rather than ATP-dependent helicases, demonstrating significant departures in RNA export mechanisms in trypanosomes.