The arabinose kinase, ARA1, gene of Arabidopsis is a novel member of the galactose kinase gene family

The arabinose-sensitive aral-l mutant of Arabidopsis is deficient in arabin ose kinase activity. A candidate for the ARA1 gene, ISA1, has been previous ly identified through the Arabidopsis genome sequencing initiative. Here we demonstrate that (1) the ARA1 gene coincides with ISA1 in a positional clo ning strategy; (2) there are mutations in the ISA1 gene in both the ara1-1 mutant and an intragenic suppressor mutant; and (3) the ara1-1 and suppress or mutant phenotypes can be complemented by the expression of the ISA1 cDNA in transgenic plants. Together these observations confirm that ISA1 is the ARA1 gene. ARA1 is a member of the galactose kinase family of genes and re presents a new substrate specificity among this and other families of sugar kinases. A second gene with similarities to members of the galactose kinas e gene family has been identified in the EST database. A 1.8 kb cDNA contai ned an open reading-frame predicted to encode a 496 amino acid polypeptide. The GAL1 cDNA was expressed in a galK mutant of Escherichia coli and in vi tro assays of extracts of the strain expressing GAL1 confirmed that the cDN A encodes a galactose kinase activity. Both GAL1 and ARA1 cross-hybridise a t low stringency to other sequences suggesting the presence of additional m embers of the galactose kinase gene family.