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We have characterized two isoforms of ATP-phosphoribosyl transferase (ATP-PRT) from Arabidopsis (AtATP-PRT1 [accession no. AB025251] and AtATP-PRT2), catalyzing the first step of the pathway of hisidine (His) biosynthesis. The primary structures deduced from AtATP-PRT1 and AtATP-PRT2 cDNAs share an overall amino acid identity of 74.6% and contain N-terminal chloroplast transit peptide sequences. DNA-blot analyses indicated that the ATP-PRTs in Arabidopsis are encoded by two separate genes with a closely similar gene structural organization. Both gene transcripts were detected throughout development, and protein-blot analysis revealed predominant accumulation of the AtATP-PRT proteins in Arabidopsis leaves. The His auxotrophy of a his1 mutant of Saccharomyces cerevisiae was suppressed by the transformation with AtATP-PRT1 and AtATP-PRT2 cDNAs, indicating that both isoforms are functionally active ATP-PRT enzymes. The K(m) values for ATP and phosphoribosyl pyrophosphate of the recombinant AtATP-PRT proteins were comparable to those of the native ATP-PRTs from higher plants and bacteria. It was demonstrated that the recombinant AtATP-PRTs were inhibited by L-His (50% inhibition of initial activity = 40-320 microM), suggesting that His biosynthesis was regulated in plants through feedback inhibition by L-His.

Molecular Cloning and Characterization of ATP-Phosphoribosyl Transferase from Arabidopsis, a Key Enzyme in the Histidine Biosynthetic Pathway