The protein farnesyltransferase (FTase) mediates posttranslational modification of proteins with isoprenoid lipids. FTase is a heterodimer and although the beta subunit harbors the active site, it requires the a subunit for its activity. Here we explore the other functions of the FTase alpha subunit in addition to its established role in protein prenylation. We found that in the absence of the beta subunit, the alpha subunit of FTase forms a stable autonomous dimeric structure in solution. We identify interactors of FTase alpha using mass spectrometry, followed by rapid in vitro analysis using the Leishmania tarentolae cell - free system. Vps4A was validated for direct binding to the FTase alpha subunit both in vitro and in vivo. Analysis of the interaction with Vps4A in Hek 293 cells demonstrated that FTase alpha controls trafficking of transferrin receptor upstream of this protein. These results point to the existence of previously undetected biological functions of the FTase alpha subunit that includes control of intracellular membrane trafficking. (C) 2015 Elsevier Inc. All rights reserved.