Assembly and stability of IFT-B complex and its function in BBSome trafficking

The machinery of intraflagellar transport (IFT) consists of IFT motors and the ciliary cargo adaptors including IFT-A and IFT-B complexes and BBSome. IFT-B, which is composed of IFT-B1 and IFT-B2 subcomplexes, interacts with IFT motors and IFT-A during anterograde IFT and IFT-A during retrograde IFT while it is also implicated in BBSome trafficking. However, the assembly and stability of IFT-B and its regulation of anterograde IFT and BBSome trafficking remain not clear. Here, we show that IFT38 functions in the regulation of anterograde IFT and retrograde trafficking of BBSome. Deletion of IFT-B1 or IFT-B2 subunits results in differential instability of IFT-B1 and IFT-B2. The stability of IFT-B1 and IFT-B2 is mutually dependent and mediated by the connecting tetramer IFT38/5788/52. The formation of an intact IFT-B1 and IFT-B2 is not altered by the deletion of IFT38 of IFT-B2 and IFT52 of IFT-B1, respectively. Further analysis suggests a modular pathway for IFT-B assembly.