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

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• DNA polymerase theta (Polθ) is a translesion polymerase critical for DNA double-strand break repair, especially in homologous recombination or non-homologous end joining deficient cells.
• Polθ also aids in DNA interstrand crosslink tolerance in certain organisms, making it a potential therapeutic target for cancer and other diseases.
• The functions of Polθ's helicase-like and polymerase domains are known, but its linker domain's role remains largely uncharacterized.

Purpose of the Study:

• To investigate the largely unknown functions of the linker domain of DNA polymerase theta (Polθ).
• To determine the specific requirements of the Polθ linker domain for DNA repair and organismal development.
• To elucidate whether protein interaction motifs or intrinsic amino acid properties are critical for Polθ linker function.

Main Methods:

• Utilized *Drosophila melanogaster* as a model organism to study Polθ linker domain function.
• Generated and tested mutant Polθ linker domains, including scrambled sequences, human Polθ linker fragments, and FUS protein regions.
• Assessed the impact of linker domain modifications on DNA double-strand break and interstrand crosslink tolerance, as well as egg development.

Main Results:

• The *Drosophila melanogaster* Polθ linker domain is essential for egg development and tolerance of DNA double-strand breaks and interstrand crosslinks.
• A scrambled linker domain retained DNA repair function, indicating sequence-specific interactions are not solely responsible.
• Replacing the linker with human Polθ linker or FUS protein regions failed to restore Polθ function, highlighting specific residue requirements.

Conclusions:

• The Polθ linker domain is not merely a passive structural element but plays an active role in DNA repair and development.
• Intrinsic amino acid properties within the linker domain are crucial for Polθ's function in DNA damage tolerance.
• These findings provide insights into Polθ's mechanism and potential as a therapeutic target, emphasizing the importance of the linker domain's specific sequence characteristics.