The small transmembrane E5 protein of bovine papillomavirus (BPV) transforms cells by forming a stable complex with and activating the platelet-derived growth factor beta receptor (PDGFR). The E5/PDGFR interaction is thought to involve specific physical contacts between the transmembrane domains of the two proteins. Lys499 at the extracellular juxtamembrane position and Thr513 within the transmembrane domain of the PDGFR are required for the interaction and are predicted to contact analogously positioned residues in the E5 protein. Here, mutagenic analysis of the transmembrane region of the PDGFbR was performed to further characterize the nature of the E5/PDGFR interaction. We show that the receptor transmembrane domain, with minimal extracellular and intracellular sequence, is sufficient for the interaction. In addition, we provide evidence that the polar nature of Thr513 as well as its positioning along the transmembrane alpha helix is important for the interaction. We also identify the receptor transmembrane amino acids Ile506 and Leu520 as additional requirements for the interaction. Since Lys499, Thr513, Ile506, and Leu520 all align along the same face of the predicted PDGFR transmembrane alpha helix, our data support the model that the PDGFR contacts the E5 protein via multiple amino acids along a single alpha helical interface.