CLONING AND CHARACTERIZATION OF THE GENE ENCODING IMP DEHYDROGENASE FROM ARABIDOPSIS-THALIANA

We have cloned and characterized the gene encoding inosine monophospha te dehydrogenase (IMPDH) from Arabidopsis thaliana (At). The transcrip tion unit of the At gene spans approximately 1900 bp and specifies a p rotein of 503 amino acids with a calculated relative molecular mass (M (r)) of 54 190. The gene is comprised of a minimum of four introns and five exons with all donor and acceptor splice sequences conforming to previously proposed consensus sequences. The deduced IMPDH amino-acid sequence from At shows a remarkable similarity to other eukaryotic IM PDH sequences, with a 48% identity to human Type II enzyme. Allowing f or conservative substitutions, the enzyme is 69% similar to human Type II IMPDH. The putative active-site sequence of At IMPDH conforms to t he IMP dehydrogenase/guanosine monophosphate reductase motif and conta ins an essential active-site cysteine residue.