CLONING OF A CDNA ENCODED BY A MEMBER OF THE ARABIDOPSIS-THALIANA ATPSULFURYLASE MULTIGENE FAMILY - EXPRESSION STUDIES IN YEAST AND IN RELATION TO PLANT SULFUR NUTRITION

An Arabidopsis thaliana ATP sulfurylase cDNA (ASA1), encoding a putati ve chloroplastic isoform, has been cloned by functional complementatio n of a Saccharomyces cerevisiae (met3) ATP sulfurylase mutant which al so has a poor sulfate transport capacity. Homologous complementation o f the yeast mutant with the ATP sulfurylase gene restores both ATP sul furylase function and sulfate transport. Heterologous complementation restores only ATP sulfurylase function as demonstrated by low [S-35]su lfate influx measurements and selenate resistance. A structural relati onship between ATP sulfurylase and sulfate membrane transporters in ye ast is proposed. The sequence of ASA1 is homologous to deduced plant a nd animal ATP sulfurylase sequences. Analyses indicate a potential tyr osine phosphorylation site which is unique to higher eukaryote sequenc es, ASA1 is specified by a single copy gene that is part of a multigen e family in A. thaliana. At least two ASA1 copies are found in Brassic a napus plants. ASA1 transcripts were found in all organs examined, wi th the highest transcript abundance and ATP sulfurylase activity in le aves or cotyledons. Absence of sulfate from culture media transiently increased B. napus transcript abundance, indicating that initially, th e response to sulfate deprivation is transcriptionally regulated.