Molecular cloning and characterization of a cDNA encoding soybean nodule IMP dehydrogenase

Inosine monophosphate dehydrogenase (IMPDH) catalyzes the rate-limiting step in de novo purine biosynthesis and is a postulated key enzyme in nitrogen assimilation in ureide-exporting nodules. A 2016 bp cDNA for IMPDH. designated as IMPDH, was cloned from a soybean nodule cDNA library. IMPDH encodes a polypeptide of 502 amino acids with a predicted molecular weight of 53 000 and a pI of 5.54, The deduced IMPDH is 70.5%, identical to that in Arabidopsis. with a 100% homology in the putative active-site region. Expressing the cloned cDNA in Escherichia coli mutant strain KLC381 (Delta guaB) restored IMPDH activity, permitting bacterial growth on minimal medium. Southern blot analysis suggested a single copy of IMPDH gene in the soybean genome. Northern blot analysis showed that the expression of IMPDH gene is apparently nodule-specific. (C) 2001 Elsevier Science B.V. All rights reserved.