World economies depend on the availability of natural rubber for industrial purposes. Despite its economic importance surprisingly little is known about rubber biogenesis in higher plants. Rubber is produced in numerous species but mechanisms of its synthesis are poorly understood. The enzyme rubber transferase (RuT) (E.C. 188.8.131.52), a prenyltransferase, causes the unique cis-polymerization of isoprene responsible for rubber accumulation in plants. Our studies will protein (RPP), the most abundant protein of guayule rubber particles. The function of RPP in rubber biogenesis will be addressed because its abundance suggests that it plays an important role either in biosynthesis stabilization, solubilization or trafficking of rubber particles. Prevailing evidence suggesting that RPP is guayule RuT must be confirmed with newly available molecular probes. A cDNA clone for RPP, recently identified in the lab, will be used to elucidate its role in rubber biogenesis. Full-length RPP clones will be examined for the effect of their expression in various heterologous and homologous systems. Biochemical analysis and enzymatic assays will compare RPP expression with putative RuT and prenyl transferase activity in those systems. Partial clones of RPP expressed as fusion proteins in E. Coli will be used to generate de-glycosylated RPP Suitable for antibody production. Antisera prepared against recombinant RPP will be used several fold; first, to measure inhibition of prenyltransferase activity in in vitro assays; second, to detect for the presence of RPP- liked proteins in other rubber-producing species and finally, for immunocytochemical studies in guayule and in transgenic plants. If RPP proves to be RuT, then engineering of rubber synthesis may be possible in other systems. %%% The production of rubber results from chemical processing of the sap from the rubber tree which cannot be grown in the USA. However another plant native to the USA, guayule, produces rubber but it is difficult to extract the compound easily from the plant. Rubber is an interesting chemical biomaterial and finding and characterizing the enzyme responsible for its synthesis is the research which is funded here. The isolation of the rubber particle protein in the plant and its purification will lead to molecular biological studies fundamental to producing rubber and related compounds in greater yields and in other plants.