RAB1B is a small GTPase that functions as a key regulator of intracellular membrane trafficking, cycling between inactive GDP-bound and active GTP-bound states to recruit effector proteins 1. Its primary roles include regulating ER-to-Golgi vesicular transport and maintaining proper Golgi morphology 2. RAB1B operates through multiple mechanisms: it recruits DGAT2 to facilitate lipid droplet growth 3, enhances TMED10-mediated unconventional protein secretion at the ERGIC 4, and functions as an effector of membrane proteins like GOLPH3 5. RAB1B activity is regulated by GAP proteins including TBC1D22B and TBC1D20 63. Clinically, RAB1B dysfunction has significant disease implications. Mutations in TBC1D20 (a RAB1B GAP) cause Warburg Micro syndrome, with evidence of impaired lipid droplet metabolism in patient fibroblasts 3. RUNX1 haplodeficiency reduces RAB1B expression, impairing ER-to-Golgi transport and von Willebrand factor trafficking in megakaryocytes, contributing to platelet dysfunction 7. RAB1B also plays critical roles in viral infections: inhibiting RAB1B impairs SARS-CoV-2 spike protein trafficking and maturation 8. Elevated TBC1D22B-mediated RAB1B inactivation in breast cancer promotes oncogenic transcriptional programs and tumor growth 6, while increased RAB1B expression modulates gene transcription and TSH response in thyroid cells 9.