A conserved C-terminal RG motif in the NgBR subunit of -prenyltransferase is critical for prenyltransferase activity.

-Prenyltransferases (-PTs) constitute a large family of enzymes conserved during evolution and present in all domains of life. In eukaryotes and archaea, -PT is the first enzyme committed to the synthesis of dolichyl phosphate, an obligate lipid carrier in protein glycosylation reactions. The homodimeric bacterial enzyme, undecaprenyl diphosphate synthase, generates 11 isoprene units and has been structurally and mechanistically characterized in great detail. Recently, we discovered that unlike undecaprenyl diphosphate synthase, mammalian -PT is a heteromer consisting of NgBR (Nus1) and hCIT (dehydrodolichol diphosphate synthase) subunits, and this composition has been confirmed in plants and fungal -PTs. Here, we establish the first purification system for heteromeric -PT and show that both NgBR and hCIT subunits function in catalysis and substrate binding. Finally, we identified a critical RG sequence in the C-terminal tail of NgBR that is conserved and essential for enzyme activity across phyla. In summary, our findings show that eukaryotic -PT is composed of the NgBR and hCIT subunits. The strong conservation of the RG motif among NgBR orthologs indicates that this subunit is critical for the synthesis of polyprenol diphosphates and cellular function.