The human DINB1 gene encodes the DNA polymerase Polθ

The humanDINB1 gene shares a high degree of homology with theEscherichia coli dinB gene. Here, we purify thehDINB1- encoded protein and show that it is a DNA polymerase. Because hDinB1 is the eighth eukaryotic DNA polymerase to be described, we have named it DNA polymerase (Pol) θ. hPolθ is unable to bypass acis-syn thymine–thymine dimer, nor does it bypass a (6–4) photoproduct or an abasic site. We also examine the fidelity of hPolθ on nondamaged DNA templates by steady-state kinetic analyses and find that hPolθ misincorporates deoxynucleotides with a frequency of about 10−3 to 10−4 . We discuss the relationship between the fidelity of hPolθ and its inability to bypass DNA damage.