We discovered that mouse oocytes contain novel non-membrane-bound organelles, which we named EndoLysosomal Vesicular Assemblies (ELVAs). ELVAs contain endolysosomal and autophagy vesicles, as well as proteasomes. In immature oocytes, ELVAs store ubiquitinated proteins and show little degradative activity. During oocyte maturation, ELVAs increase protein degradation, thereby degrading the stored proteins. To understand which proteins are being degraded inside ELVAs during oocyte maturation we treated mouse oocytes with or without the lysosomal inhibitor Bafilomycin A1 (BafA1) during maturation and subjected equal number of in vitro matured oocytes to mass spec, looking for enriched proteins in the BafA1-treated sample.