cDNA Cloning and Expression of a Gene for Isocitrate Lyase in Pumpkin Cotyledons

A cDNA clone for isocitrate lyase (ICL) was isolated from a cDNA library prepared from the poly(A)+ RNA of etiolated pumpkin cotyledons. The cDNA encoded a poly-peptide with 576 amino acids, whose sequence is more than 79 % identical to those of ICL from other higher plants and contains the C-terminal tripeptide, Ser-Arg-Met, which is a putative targeting signal to microbodies. Immunogold anal-ysis revealed that ICL protein is exclusively localized in mi-crobodies in etiolated pumpkin cotyledons. Double label-ing experiments with protein A-gold particles of different sizes showed that ICL protein coexists with a leaf-per-oxisomal enzyme, glycolate oxidase, in the microbodies of greening and senescing pumpkin cotyledons, indicating that transformation between glyoxysomes and leaf per-oxisomes occurs directly during greening and senescenc