Zebrafish Pol-Theta and Human Pol-Theta, Orthologues with Homologous Function

DNA Polymerase Theta (Pol {theta}) is a conserved an A-family polymerase that plays an essential role in repairing double strand breaks, through micro-homology end joining, and bypassing DNA lesions, through translesion synthesis, to protect genome integrity. Despite its essential role in DNA repair, Pol {theta} is inherently error-prone. Recently, key loop regions were identified to play an important role in key functions of Pol {theta}. Here we present a comparative structure-function study of the polymerase domain of zebrafish and human Pol {theta}. We show that these two proteins share a large amount of sequence and structural homology. However, we identify differences in the amino acid composition within the key loop areas shown to drive characteristic Pol {theta} functions. Despite these differences zebrafish Pol {theta} still displays characteristics identify in human Pol {theta}, including DNA template extension in the presence of different divalent metals, microhomology-mediated end joining, and translesion synthesis. These results will support future studies looking to gain insight into Pol {theta} function on the basis of evolutionarily conserved features.