An intact cDNA from Arabidopsis thaliana for adenine phosphoribosyltransferase (APRT) was isolated and sequenced. The cDNA is 729 nucleotides in length and predicts a protein of Mr 27,140. The deduced amino acid sequence has been compared with those of other APRTs and shown to be most similar to the Escherichia coli protein. Construction of a molecular tree of the known APRT amino acid sequences indicates the A. thaliana and E. coli APRT sequences form one cluster and the currently available vertebrate and invertebrate sequences form a separate grouping. Since it is possible to select either for or against the expression of APRT, the isolation of this APRT cDNA clone will allow these selection schemes to be used in plant genetic experiments.