Abstract
ATP sulfurylase, the first enzyme in the sulfate assimilation pathway of plants, catalyzes the formation of adenosine phospho-sulfate from ATP and sulfate. Here we report the cloning of a cDNA encoding ATP sulfurylase (APS1) from Arabidopsis thalian a. APSl was isolated by its ability to alleviate the methionine requirement of an ATP sulfurylase mutant strain of Saccharomyces cerevisiae (yeast). Expression of APSl correlated with the presence of ATP sulfurylase enzyme activity in cell extracts. APSl is a 1748-bp cDNA with an open reading frame predided to encode a 463-amino acid, 51,372-D protein. The predicted amino acid sequence of APSl is similar to ATP sulfurylase of S. cerevisiae , with which it is 25% identical. Two lines of evidence indicate that APSl encodes a chloroplast form of ATP sulfurylase. Its predicted amino-terminal sequence resembles a chloroplast transit peptide; and the APSl polypeptide, synthesized in vitro, is capable of entering isolated intact chloroplasts. Several genomic DNA fragments that hybridize with the APSl probe were identified. The APSl cDNA hybridizes to three species of mRNA in leaves (1.85, 1.60, and 1.20 kb) and to a single species of mRNA in roots (1.85 kb).