Natural rubber fromHevea brasiliensisis a high molecular mass polymer of isoprene units withcis-configuration. The enzyme responsible for the cis-1,4-polymerization of iso-prene units has been identified as a particle-bound rubber transferase, but no gene encoding this enzyme has been cloned from rubber-producing plants. By using sequence information from the conserved regions of cis-prenyl chain elongating enzymes that were cloned recently, we have iso-lated and characterized cDNAs from H.