Geranylgeranyl diphosphate synthase from Scoparia dulcis and Croton sublyratus. Plastid localization and conversion to a farnesyl diphosphate synthase by mutagenesis

cDNAs encoding geranylgeranyl diphosphate synthase (GGPPS) of two diterpene -producing plants. Scoparia dulcis and Croton sublyratus, have been isolate d using the homology-based polymerase chain reaction (PCR) method. Both clo nes contained highly conserved aspartate-rich motifs (DDXX(XX)D) and their N-terminal residues exhibited the characteristics of chloroplast targeting sequence. When expressed in Escherichia coli, both the full-length and trun cated proteins in which the putative targeting sequence was deleted catalyz ed the condensation of farnesyl diphosphate and isopentenyl diphosphate to produce geranylgeranyl diphosphate (GGPP). The structural factors determini ng the product length in plant GGPPSs were investigated by constructing S. dulcis GGPPS mutants on the basis of sequence comparison with the first asp artate-rich motif (FARM) of plant farnesyl diphosphate synthase. The result indicated that in plant GGPPSs small amino acids, Met and Ser, at the four th and fifth positions before FARM and Pro and Cys insertion in FARM play e ssential roles in determination of product length. Further, when a chimeric gene comprised of the putative transit peptide of the S. dulcis GGPPS gene and a green fluorescent protein was introduced into Arabidopsis leaves by particle gun bombardment, the chimeric protein was localized in chloroplast s, indicating that the cloned S. dulcis GGPPS is a chloroplast protein.