Deletion mutants of AP-1 adaptin subunits display distinct phenotypes in fission yeast

Abstract

Adaptins are subunits of the heterotetrameric (β/μ/γ/ σ) adaptor protein (AP) complexes that are involved in clathrin-mediated membrane trafficking. Here, we show that in Schizosaccharomyces pombe the deletion strains of each individual subunit of the AP-1 complex [Apl2 (β), Apl4 (γ), Apm1 (μ) and Aps1 (σ)] caused distinct phenotypes on growth sensitivity to temperature or drugs. We also show that the Δ apm1 and Δ apl2 mutants displayed similar but more severe phenotypes than those of Δ aps1 or Δ apl4 mutants. Furthermore, the Δ apl2 Δ aps1 and Δ apl2 Δ apl4 double mutants displayed synthetic growth defects, whereas the Δ aps1 Δ apl4 and Δ apl2 Δ apm1 double mutants did not. In pull-down assay, Apm1 binds Apl2 even in the absence of Aps1 and Apl4, and Apl4 binds Aps1 even in the absence of Apm1 and Apl2. Consistently, the deletion of any subunit generally caused the disassociation of the heterotetrameric complex from endosomes, although some subunits weakly localized to endosomes. In addition, the deletion of individual subunits caused similar endosomal accumulation of v-SNARE synaptobrevin Syb1. Altogether, results suggest that the four subunits are all essential for the heterotetrameric complex formation and for the AP-1 function in exit transport from endosomes. © Journal compilation © 2009 by the Molecular Biology Society of Japan/Blackwell Publishing Ltd.