ISOPRENYLATION OF PLANT-PROTEINS IN-VIVO - ISOPRENYLATED PROTEINS AREABUNDANT IN THE MITOCHONDRIA AND NUCLEI OF SPINACH

Protein isoprenylation in vivo is demonstrated using spinach seedlings labeled with [H-3]mevalonate, This report provides evidence for the o ccurrence of a large number of isoprenylated proteins in plants. Seedl ings, without roots, were labeled quantitatively through the cut stem. Mevinolin treatment of the seedlings resulted in increased incorporat ion of radiolabel into proteins. Approximately 30 labeled bands could be detected after autoradiography of SDS-polyacrylamide gel electropho resis-separated polypeptides, ranging in molecular mass from 6 to 200 kDa, Methyl iodide hydrolysis resulted in the release of covalently bo und farnesol, geranylgeraniol, phytol, and some unidentified isoprenoi d compounds from mevalonate-labeled proteins, It was found that all ce llular fractions contained some isoprenylated proteins, although most were located in the mitochondria and nuclei. Subfractionation of the n ucleus revealed that the majority of isoprenylated proteins in this co mpartment were components of the nuclear matrix. The results demonstra te that in vivo labeling of a complex organism can be performed using a plant system in order to study protein isoprenylation and distributi on of modified proteins in different cellular compartments.