Y. Shima et al., CONSTRUCTION AND CHARACTERIZATION OF N-TERMINALLY TRUNCATED DNA-POLYMERASE FROM THERMUS-THERMOPHILUS, Journal of fermentation and bioengineering, 81(6), 1996, pp. 504-510
Various plasmids harboring the truncated DNA polymerase gene (polA) fr
om Thermus thermophilus HB8 (Tth polymerase) were constructed. The mos
t thermostable Tth Delta NF2 polymerase [the gene product of polA Delt
a NF2, which lacked a 751-bp region (region flanked by initiation codo
n and FspI site in the polA gene)] was selected, and purified from the
recombinant Escherichia coli. SDS polyacrylamide gel electrophoresis
revealed that the molecular weight of the Tth Delta NF2 polymerase is
58-61 kDa, which is approximately 30 kDa smaller than that of the wild
-type enzyme. The specific activity of the 5'to-3' polymerization of t
he Tth Delta NF2 polymerase was 63% of that of the Tth polymerase. How
ever, no 5'-to-3' exonuclease activity was detected in this mutant enz
yme (less than 1% of the specific activity of wild-type enzyme). The a
ctivities of the wild-type and mutant enzymes were maximal at 75 degre
es C. Approximately 50% of the enzyme activity was retained even after
heat treatment of the Tth Delta NF2 polymerase at 70 degrees C for 2
h, but the thermostability of the mutant enzyme was slightly lower tha
n that of the wild-type enzyme. Both the Tth Delta NF2 and Tth polymer
ases were capable of non-templated addition of deoxyribonucleotide to
a 3'-hydroxyl group of blunt-ended DNA.