Enzymes identified using genomic DNA sequences suggest some atypical characteristics of de novo biosynthesis of purines in archaebacteria

Genes coding for enzymes that are expected to be involved in de novo biosynthesis of nucleotides have been identified using the complete genomic DNA sequences of 7 archaebacteria. By the identified enzymes of Aeropyrum pernix, no step is expected to be mediated in the pathway leading to IMP, starting from the initial metabolic precursors, 5-phosphoribosyl-1-pyrophosphate and glutamine. Thus, an atypical pathway is needed to synthesize IMP in this archaebacterium. Of any of the 7 archaebacteria, no gene is identified to code for the enzymatic activity of synthesizing GDP from GMP. Unidentified types of enzymes are expected to mediate this and some other essential steps, whose corresponding enzymes are missing from some of the archaebacteria. The identified archaebacterial enzymes are, in general, closer to enzymes of E. coli than to those of yeast, in particular, in terms of the numbers of polypeptides composing these enzymes.