Abstract
The first step of methionine biosynthesis in higher plants, the condensation of O-phosphohomoserine
and L-cysteine forming the thioether Cystathionine, is catalyzed by the enzyme Cystathionine
γ-synthase (CgS). We have isolated a cDNA encoding CgS from a leaf λ ZAP II-library
of Solanum tuberosum L. The nucleotide and deduced amino acid sequence showed homology to the other CgS
sequences from Arabidopsis thaliana, Zea mays, Mesembryanthemum crystallinum and Fragaria vesca. The truncated cDNA without putative leader peptide, when cloned into a bacterial
expression vector, complemented the E. coli metB1 mutant strain LE392. Enzyme activity of the potato CgS and E. coli metB were comparable in the auxotrophic background. Transcript levels of CgS in different
tissues of potato plants were determined by Northern blot analysis. Expression was
found in all tissues with elevated levels in flowers and source leaves. The pattern
of gene expression during a day/night period implied light-dependent control of CgS
transcription typical for enzymes localized in plastids. The expression of CgS was
shown to be light-inducible.
Key words
Cystathionine gamma-synthase - methionine biosynthesis -
Solanum tuberosum
