ABSTRACT
A structural model for plant 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) has been proposed on the basis of primary sequence comparisons. In order to define the topology of Arabidopsis HMGR in the estrogen receptor membranes, posttranslation analysis involving digestion with proteinase K is performed, in combination with fractionation of the microsomal vesicles. Sequence analysis of the radish cDNA insert of plasmid pYRS10, conferring ergosterol-autotrophy and thermoresistance to the yeast strain KV5, revealed the existence of an open reading frame containing the entire coding unit for a protein of about 42 kDa, in agreement to thiolase proteins from other organisms. The accumulation of plastid prenyl lipids such as carotenoids, chlorophylls, plastoquinone, phylloquinone, and a-tocopherol was not inhibited by mevinolin, which was interpreted to mean that the compound cannot penetrate the plastid envelope and thus cannot inhibit the putative plastid HMGR isozyme. In order to demonstrate the importance of an intact mevalonic acid biosynthesis we have used highly synchronizable tobacco BY-2 cells.
