Cloning, characterization and sequence comparison of the gene coding for IMP dehydrogenase from Pyrococcus furiosus

Purine and pyrimidine biosynthesis in higher plants

Purine and pyrimidine nucleotides have important functions in a multitude of biochemical and developmental processes during the life cycle of a plant. In higher plants the processes of nucleotide metabolism are poorly understood, but it is in principle accepted that nucleotides are essential constituents of fundamental biological functions. Despite of its significance, higher plant nucleotide metabolism has been poorly explored during the last 10-20 years (Suzuki and Takahashi 1977, Schubert 1986, Wagner and Backer 1992). But considerable progress was made on purine biosynthesis in nodules of ureide producing tropical legumes, where IMP-synthesis plays a dominant role in primary nitrogen metabolism (Atkins and Smith 2000, Smith and Atkins 2002). Besides these studies on tropical legumes, this review emphasises on progress made in analysing the function in planta of genes involved in purine and pyrimidine biosynthesis and their impact on metabolism and development.

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 53000 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 (DeltaguaB) 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.

Archaea and the prokaryote-to-eukaryote transition

Since the late 1970s, determining the phylogenetic relationships among the contemporary domains of life, the Archaea (archaebacteria), Bacteria (eubacteria), and Eucarya (eukaryotes), has been central to the study of early cellular evolution. The two salient issues surrounding the universal tree of life are whether all three domains are monophyletic (i.e., all equivalent in taxanomic rank) and where the root of the universal tree lies. Evaluation of the status of the Archaea has become key to answering these questions. This review considers our cumulative knowledge about the Archaea in relationship to the Bacteria and Eucarya. Particular attention is paid to the recent use of molecular phylogenetic approaches to reconstructing the tree of life. In this regard, the phylogenetic analyses of more than 60 proteins are reviewed and presented in the context of their participation in major biochemical pathways. Although many gene trees are incongruent, the majority do suggest a sisterhood between Archaea and Eucarya. Altering this general pattern of gene evolution are two kinds of potential interdomain gene transferrals. One horizontal gene exchange might have involved the gram-positive Bacteria and the Archaea, while the other might have occurred between proteobacteria and eukaryotes and might have been mediated by endosymbiosis.