Npl3 is required for efficient autophagosome-vacuole fusion

Macroautophagy/autophagy is a highly conserved catabolic membrane trafficking process through which various intracellular constituents, from proteins to organelles, are targeted for vacuolar/lysosomal degradation. Autophagy is tightly regulated both temporally and in magnitude at multiple levels to prevent either excessive or insufficient activity. To date, only a few RNA-binding proteins have been characterized as regulating the expression of genes essential for autophagy, and the contribution of post-transcriptional regulation in autophagy activity remains poorly understood. Here, through a genetic screen for autophagy-defective mutants, we identified Npl3, a nucleus-cytoplasm shuttling mRNA-binding protein, as essential for both bulk and selective types of autophagy. Deletion of NPL3 does not affect autophagosome biogenesis, closure, or maturation; however, it severely impairs autophagosome-vacuole fusion and results in minimal autophagosome turnover. We further demonstrated that this regulation depends on the RNA-binding domain of Npl3 and its capability for nuclear re-import. Together, our results reveal a novel layer of post-transcriptional regulation of autophagy. Abbreviations: Atg,autophagy related; HOPS: homotypic fusion and protein sorting; prApe1: precursor aminopeptidase I; RBP, RNA-binding protein; RRM, RNA-recognition motif; SNARE: soluble NSF attachment protein receptor; PAS: phagophore asse