FAM125B Full-Length MS Protein Standard (NP_001011703), Labeled with [U- 13C6, 15N4]-L-Arginine and [U- 13C6, 15N2]-L-Lysine, was produced in human 293 cells (HEK293) with fully chemically defined cell culture medium to obtain incorporation efficiency at Creative-Proteomics. The protein encoded by this gene is a component of the ESCRT-I complex, a heterotetramer, which mediates the sorting of ubiquitinated cargo protein from the plasma membrane to the endosomal vesicle. ESCRT-I complex plays an essential role in HIV budding and endosomal protein sorting. Depletion and overexpression of this and related protein (MVB12A) inhibit HIV-1 infectivity and induce unusual viral assembly defects, indicating a role for MVB12 subunits in regulating ESCRT-mediated virus budding. Alternatively spliced transcript variants encoding different isoforms have been found for this gene.