UBL4A is a ubiquitin-like protein that functions as a core component of the BAG6/BAT3 cytosolic quality control complex, maintaining misfolded and hydrophobic proteins in a soluble state 1. As part of this complex, UBL4A mediates post-translational delivery of tail-anchored proteins to the endoplasmic reticulum (ER) membrane through interactions with SGTA and ASNA1 2. Proteins failing proper ER delivery are ubiquitinated by UBL4A-dependent mechanisms and sorted to the proteasome for degradation 3. UBL4A also participates in ER-associated degradation (ERAD), maintaining retrotranslocated proteins in soluble form for proteasomal targeting 4. Beyond protein quality control, UBL4A exhibits diverse cellular functions. It promotes K63-linked ubiquitination of TRAF6 to enhance antiviral innate immunity and type I interferon production 5. UBL4A suppresses autophagy-mediated pancreatic cancer proliferation and metastasis by directly interacting with lysosomal protein LAMP1 6. In DNA damage response, the nuclear BAG6-UBL4A-GET4 complex mediates cell death signaling through BRCA1 recruitment 7. Additionally, UBL4A interacts with the Arp2/3 complex through its C-terminus to regulate actin dynamics and cell death 8. Recent evidence indicates UBL4A protects against sepsis-associated acute kidney injury through miR-205-5p regulation 9, and its activity is regulated by the deubiquitinase USP13 to maintain BAG6 functionality 10.