CLONING, CHARACTERIZATION AND SEQUENCE COMPARISON OF THE GENE CODING FOR IMP DEHYDROGENASE FROM PYROCOCCUS-FURIOSUS

We have cloned and characterized the gene encoding inosine monophospha te dehydrogenase (IMPDH) from Pyrococcus furiosus (PS), a hyperthermop hillic archeon. Sequence analysis of the Pf gene indicated an open rea ding frame specifying a protein of 485 amino acids (aa) with a calcula ted M(r) of 52900. Canonical Archaea promoter elements, Box A and Box B, are located -49 and -17 nucleotides (nt), respectively, upstream of the putative start codon. The sequence of the putative active-site re gion conforms to the IMPDH signature motif and contains a putative act ive-site cysteine. Phylogenetic relationships derived by using all ava ilable IMPDH sequences are consistent with trees developed for other m olecules; they do not precisely resolve the history of Pf IMPDH but in dicate a close similarity to bacterial IMPDH proteins. The phylogeneti c analysis indicates that a gene duplication occurred prior to the div ision between rodents and humans, accounting for the Type I and II iso forms identified in mice and humans.