ISOLATION AND CHARACTERIZATION OF 2 CDNAS ENCODING FOR COMPARTMENT-SPECIFIC ISOFORMS OF O-ACETYLSERINE (THIOL) LYASE FROM ARABIDOPSIS-THALIANA

cDNAs encoding for two isoforms of O-acetylserine (thiol) lyase (OAS-T L), which catalyzes the synthesis of cysteine, have been isolated from Arabidopsis thaliana. Secondary structure together with expression pa tterns derived during photomorphogenesis indicate cellular localizatio ns in the cytosol and plastids, thus allowing a direct comparison of c ompartment-specific forms within one species. The cytosolic OAS-TL com plemented an E. coli auxotrophic mutant lacking cysteine synthesis. Bo th isoforms are represented by small gene families. They are expressed under all conditions investigated and were observed to increase in ex pression in plants grown with limited sulfate supply.