CHARACTERIZATION OF AN ARABIDOPSIS-THALIANA CDNA-ENCODING AN S-ADENOSYLMETHIONINE-SENSITIVE THREONINE SYNTHASE - THREONINE SYNTHASE FROM HIGHER PLANTS

An Arabidopsis thaliana cDNA encoding an S-adenosylmethionine-sensitiv e threonine synthase (EC 4.2.99.2) has been isolated by functional com plementation of an Escherichia coli mutant devoid of threonine synthas e activity. Threonine synthase from A. thaliana was shown to be synthe sized with a transit peptide. The recombinant protein is activated by S-adenosylmethionine in the same range as the plant threonine synthase and evidence is presented for an involvement of the N-terminal part o f the mature enzyme in the sensitivity to S-adenosylmethionine.