The human DINB1 gene encodes the DNA polymerase Polθ

The human DINB1 gene shares a high degree of homology with the Escherichia coli dinB gene. Here, we purify the hDINB1-encoded protein and show that it is a DMA polymerase. Because hDinB1 is the eighth eukaryotic DNA polymerase to be described, we have named it DNA polymerase (Pol) theta. hPol theta is unable to bypass a cis-syn thymine-thymine dimer, nor does it bypass a (6-4) photoproduct or an abasic site. We also examine the fidelity of hPol theta on nondamaged DNA templates by steady-state kinetic analyses and find that hPol theta misincorporates deoxynucleotides with a frequency of about 10(-3) to 10(-4). We discuss the relationship between the fidelity of hPol theta and its inability to bypass DNA damage.