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Abstract
Cargo adapters link various large flagellar building blocks to intraflagellar transport (IFT) trains, ensuring transport from the cell body to the ciliary tip for assembly. However, it remains largely unknown how these adapters interact with IFT trains, their cargo, and how these interactions are regulated. Using Chlamydomonas reinhardtii, we show that ARMC2, the adapter for the radial spoke precursor complex (RS-PC), binds to IFT via its N-terminal intrinsically disordered domain and that the C-terminal ARM domain is necessary to bind to the RS-PC. IFT of ARMC2 and the RS-PC are rarely observed in full-length cilia but are significantly upregulated during ciliary assembly. Remarkably, The IDR alone (ARMC21-411) of ARMC2 displays frequent IFT events in full length cilia. We also show by yeast-two-hybrid analysis that ARMC2’s N- and C-terminal domains interact. Taken together we propose an autoinhibitory model for ARMC2 that regulates IFT of radial spokes.