9408031 Leustek Two enzymes, ATP sulfurylase and APS kinase, catalyze the activation of sulfate in plants leading to the synthesis of sulfur containing compounds vital for cell function. Isoenzymes of ATP sulfurylase are compartmentalized in chloroplasts, mitochondria and the cytosol, suggesting that they may play distinct physiological roles in sulfur metabolism. The objective of this research is to study the expression of the isoenzymes in order to establish a molecular basis for the control of sulfate activation. cDNAs encoding the sulfate activating enzymes were cloned from Arabidopsis thaliana by complementation of Saccharomyces cerevisiae ATP sulfurylase, met3, or APS kinase, met14, mutants. Four members of the ATP sulfurylase gene family and one encoding APS kinase have been isolated. It is proposed to further characterize these cDNAs and to study their expression and function in A. thaliana and Brassica juncea. Since sulfur-containing peptides play a significant role in resistance to heavy metals, the influence of heavy metal exposure will be investigated on expression of ATP sulfurylase and APS kinase. These studies will help advance our understanding of plant metabolism, growth, development and response to stress. ***
