DmGEN shows a flap endonuclease activity, cleaving the blocked-flap structure and model replication fork

Area of Science:

• Molecular Biology
• Biochemistry
• Genetics

Background:

• The RAD2/XPG endonuclease family plays crucial roles in DNA repair and replication.
• Existing classifications include class I (XPG), class II (FEN-1), and class III (EXO-1) nucleases.
• The precise enzymatic properties and classification of Drosophila melanogaster XPG-like endonuclease (DmGEN) remained uncharacterized.

Purpose of the Study:

• To biochemically characterize Drosophila melanogaster XPG-like endonuclease (DmGEN).
• To determine the substrate specificity and nuclease activities of DmGEN.
• To establish the classification of DmGEN within the RAD2/XPG nuclease family.

Main Methods:

• Site-directed mutagenesis to create an active-site mutant (E143A E145A) of DmGEN.
• In vitro assays to assess flap endonuclease and 5'-3' exonuclease activities.
• Analysis of DmGEN's interaction with model DNA structures, including bubble structures and replication forks.
• Immunostaining to determine the subcellular localization of DmGEN in Drosophila embryos.

Main Results:

• DmGEN exhibits flap endonuclease activity, preferring blocked-flap substrates, distinguishing it from FEN-1.
• DmGEN possesses weak nick-dependent 5'-3' exonuclease activity.
• DmGEN cleaves the lagging strand of a model replication fork but cannot incise bubble structures, unlike XPG.
• DmGEN localizes to the nucleus in actively proliferating Drosophila embryos.

Conclusions:

• DmGEN represents a new class (class IV) within the RAD2/XPG nuclease family based on its unique biochemical properties.
• DmGEN's distinct substrate preference and cleavage activity suggest a specialized role in DNA processing during replication.
• The nuclear localization of DmGEN in proliferating cells highlights its potential involvement in DNA replication or repair pathways in Drosophila.