H2O + IMP + NAD(+) = H(+) + NADH + XMP Purine metabolism; XMP biosynthesis via de novo pathway; XMP from IMP: step 1/1. Homotetramer. Belongs to the IMPDH/GMPR family. Could be the product of a pseudogene unlikely to encode a functional protein. In strain S288c, this gene has a frameshift compared to the other IMD alleles, producing 2 ORFs YAR073W and YAR075W. Additionally, YAR073W is not transcribed and lacks the biological functions of the other IMD genes even when artificially expressed. Because of that it is not part of the S.cerevisiae S288c complete/reference proteome set.