THE ARABIDOPSIS-THALIANA FPS1 GENE GENERATES A NOVEL MESSENGER-RNA THAT ENCODES A MITOCHONDRIAL FARNESYL-DIPHOSPHATE SYNTHASE ISOFORM

The enzyme farnesyl-diphosphate synthase (FPS; EC 2,5,1.1,/EC 2.5.1.10 ) catalyzes the synthesis of farnesyl diphosphate from isopentenyl dip hosphate and di methylallyl diphosphate, FPS is considered to play a k ey role in isoprenoid biosynthesis, We have reported previously that A rabidopsis thaliana contains two differentially expressed genes, FPS1 and FPS2, encoding two highly similar FPS isoforms, FPS1 and FPS2, (Cu nillera, N., Arro, M., Delourme, D., Karst, F., Boronat, A., and Ferre r, A, (1996) J, Biol, Chem, 271, 7774-7780), In this paper we report t he characterization of a novel Arabidopsis FPS mRNA (FPS1L mRNA) deriv ed from the FPS1 gene, A cDNA corresponding to the FPS1L mRNA was clon ed using a reverse transcription-polymerase chain reaction strategy, N orthern blot analysis showed that the two FPS1-derived mRNAs are diffe rentially expressed, The FPS1L mRNA accumulates preferentially in infl orescences, whereas the previously reported FPS1 mRNA (FPS1S mRNA) is predominantly expressed in roots and inflorescences, FPS1L mRNA contai ns an inframe AUG start codon located 123 nucleotides upstream of the AUG codon used in the translation of the FPS1S isoform, Translation of the FPS1L mRNA from the upstream AUG codon generates a novel FPS1 iso form (FPS1L) with an NH2-terminal extension of 41 amino acid residues, which has all the characteristics of a mitochondrial transit peptide, The functionality of the FPS1L NH2-terminal extension as a mitochondr ial transit peptide was demonstrated by its ability to direct a passen ger protein to yeast mitochondria in vivo and by in vitro import exper iments using purified plant mitochondria, The Arabidopsis FPS1L isofor m is the first FPS reported to contain a mitochondrial transit peptide .