Isopentenyl monophosphate kinase (IPK) from Thermoplasma acidophilum DSM 1728[6 (link), 9 (link)] was codon-optimized and synthesized by Genewiz, Inc (see Supplemental Table S1). The ipk gene was PCR amplified from the synthesized template and sub-cloned into pET28a using NdeI and XhoI restriction sites to generate an N-terminally hexa-histidine tagged fusion. Briefly, PCR was performed using Phire Hot Start II polymerase (ThermoFisher) according to the supplier’s protocol, purified by agarose gel electrophoresis, digested with NdeI and XhoI, and purified again. The digested PCR product and similarly treated pET28a were ligated at room temperature with T4 ligase (New England BioLabs) according to the supplier’s protocol. The ligation mixture was then transformed into E. coli DH5α and plated onto LB agar plates containing 50 μg/mL kanamycin. Individual colonies were picked, grown in the presence of kanamycin, plasmids purified and the ipk gene sequence verified by DNA sequencing (Genewiz).