A non-tethering role for the Drosophila linker domain in promoting damage resolution

DNA polymerase theta ( $$ ) is an error-prone translesion polymerase that becomes crucial for DNA double-strand break repair when cells are deficient in homologous recombination or non-homologous end joining. In some organisms, $$ also promotes tolerance of DNA interstrand crosslinks. Due to its importance in DNA damage tolerance, $$ is an emerging target for treatment of cancer and disease. Prior work has characterized the functions of the $$ helicase-like and polymerase domains, but the roles of the linker domain are largely unknown. Here, we show that the Drosophila melanogaster $$ linker domain promotes egg development and is required for tolerance of DNA double-strand breaks and interstrand crosslinks. While a linker domain with scrambled amino acid residues is sufficient for DNA repair, replacement of the linker with part of the Homo sapiens $$ linker or a disordered region from the FUS RNA-binding protein does not restore function. These results demonstrate that the linker domain is not simply a random tether between the helicase-like and polymerase domains. Furthermore, they suggest that intrinsic amino acid residue properties, rather than protein interaction motifs, are more critical for $$ linker functions in DNA repair.