Correct Option: D

TthPlus DNA polymerase is isolated from the Thermus thermophilus strain. TthPlus DNA polymerase is a single 92 kDa polypeptide showing a 52 -32 exonuclease activity but lacking 32 -52 exonuclease activity. It catalyzes the polymerization of nucleotides into double-stranded DNA in the presence of MgCl₂. Its efficiency has been shown more particularly on large DNA fragments up to 12 kb (using lambda phage DNA as a template). TthPlus DNA polymerase is also capable of catalyzing the polymerization of DNA using a RNA template in the presence of Mn²⁺. The ability of TthPlus DNA polymerase to reverse transcribe at elevated temperatures (70 C) minimizes the problems encountered with strong secondary structures in RNA since they are unstable at higher reaction temperatures. Higher temperatures also result in increased specificity of primer hybridization and extension. In coupled RT/PCR assays, TthPlus is about 50-100 times more efficient than regular Taq DNA polymerase.