Transmembrane protein 39B (TMEM39B) is a protein that in humans is encoded by the gene TMEM39B. TMEM39B is a multi-pass membrane protein with eight transmembrane domains. The protein localizes to the plasma membrane and vesicles. The precise function of TMEM39B is not yet well-understood by the scientific community, but differential expression is associated with survival of B cell lymphoma, and knockdown of TMEM39B is associated with decreased autophagy in cells infected with the Sindbis virus. Furthermore, the TMEM39B protein been found to interact with the SARS-CoV-2 ORF9C (also known as ORF14) protein. TMEM39B is expressed at moderate levels in most tissues, with higher expression in the testis, placenta, white blood cells, adrenal gland, thymus, and fetal brain.