| Two genes encoding a NAD+-dependent DNA ligase (LigA) and an ATP-dependent DNA ligase (LigB) were identified in the genome of the extremely radioresistant bacterium. Deinococcus radiodurans (DR). This dissertation contains three aspects concerning bioinformatics, mutation and biochemical analysis of DR DNA ligases. Results are as follows:1. Phylogenetic and regional alignment of conserved sequence analysis show that DRLigA was highly related to Thermus ligases. a NAD+-dependent DNA ligase. whereas DRLigB had no significant homology with some ATP-dependent DNA ligase. other than Nitrosomonas europaea (NE1884, a possible homolog of eukaryotic DNA ligase Ⅲ).2. DRBO100 and DR2069 were both subjected to targeted mutagenesis. Mutant DRBO100 showed to be homozygous, whereas DR2069 was persistently heterozygous. Therefore, DRBO100 is considered to be a non-essential gene, but DR2069 is likely essential.3. The recombinant enzymes were expressed in Escherichia coli, purified to homogeneity and their biochemical properties were characterized. The optimal temperature and pH value of the two DNA ligases were 60℃ and 7.0, respectively. Their optimal concentration of MgCl2 was 5mM. Their half-life of heat inactivation at 100℃ were about 3 min and 5 min. respectively. In addition. DRLigB displayed higher activity than DRLigA at stick and blunt ended joining of DNA.
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