Molecular cloning and tissue expression of an insect farnesyl diphosphate synthase

The enzyme farnesyl-diphosphate synthase (FPS, EC2.5.1.1/EC2.5.1.10), which has been shown to play a key role in isoprenoid biosynthesis, catalyzes th e synthesis of farnesyl diphosphate from isopentenyl diphosphate and di-met hylallyl diphosphate. Insects do not synthesize cholesterol de novo, rather farnesyl diphosphate leads to the formation of nonsterol isoprenoids, whic h are essential for insect development and reproduction. In this paper, we describe the characterization of one FPS from the moth Agrotis ipsilon, the first insect FPS to be reported. An homologous probe was obtained through a nested PCR strategy using degenerate primers designed from the conserved domains of FPS from other organisms. The complete cDNA clone was isolated b y PCR screening of a brain cDNA library by using homologous primers deduced from the probe. Analysis of the nucleotide sequence revealed that the cDNA encodes a polypeptide of 412 amino acids (M-r = 47 170), which shares regi ons similar to the FPS of other organisms, but exhibits singularities such as an extra N-terminal extension of approximate to 70 amino acid residues U sing an RNase protection assay, a protected fragment corresponding to the r egion encoding the FPS catalytic site was found in brain, ovary, fat body a nd corpora allata samples, but not in muscle. FPS is overexpressed in the c orpora allata, the endocrine gland that produces the juvenile hormones. The se hormones are specific to insects and play a crucial role in regulating i nsect physiology.