Cloning and characterization of an inorganic pyrophosphatase gene from Arabidopsis thaliana

The Arabidopsis PPA1 gene was identified fortuitously in a screen of lambda Fix genomic library for TOP1 (topoisomerase I) clones with a Saccharomyces cerevisiae TOP1 cDNA probe. Homology resides in a 1.5 kb EcoRI fragment. This fragment was then used as a probe to isolate a single clone from a poly(A)-primed cDNA library and several clones from a random hexamer-primed cDNA library. All the clones from both cDNA libraries are approximately the same size and together span approximately 1 kb of unique sequence. However, the yeast TOP1 probe does not hybridize to the cDNA PPA1 clones, indicating that the TOP1 homology most likely resides in intron sequences.