Class E vacuolar protein sorting (Vps) mutations cause yeast to generate a novel organelle - the class E compartment - next to the vacuole. The proteins affected by these mutations function in endosomal trafficking and have relatives in mammals, including the AAA-type ATPase SKD1. To investigate SKD1 function further, Hideaki Fujita and coworkers have used two-hybrid screening to search for its binding partners. They now reveal two new mammalian class E Vps proteins that bind to SKD1: SBP1 and mVps2 (see p. 2997). Both have orthologues in yeast and are targeted to aberrant endosomal structures in cells expressing ATPase-deficient SKD1. The authors' studies indicate that mVps2 controls membrane association of SKD1 and that SKD1 regulates assembly of a large SBP1-containing complex. Interestingly, SBP1 turns out to be identical to a previously isolated protein that interacts with the lysosomal trafficking regulator Lyst, mutations in which cause Chediak-Higashi syndrome (CHS). Fujita...

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