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Updated: May 11, 2026

Reconstitution of Msp1 Extraction Activity with Fully Purified Components
Published on: August 10, 2021
A cryptic targeting signal creates a mitochondrial FEN1 isoform with tailed R-Loop binding properties
Lawrence Kazak1, Aurelio Reyes, Jiuya He
1MRC-Mitochondrial Biology Unit, Wellcome Trust-MRC Building, Cambridge, United Kingdom.
A new mitochondrial Flap endonuclease 1 (FEN1) isoform, FENMIT, is generated by alternative translation. This isoform targets mitochondria and interacts with RNA/DNA hybrids, impacting mitochondrial DNA replication.
Area of Science:
- Mitochondrial biology
- Molecular genetics
- DNA repair
Background:
- Flap endonuclease 1 (FEN1) is a key DNA repair and replication protein.
- FEN1 is typically found in the nucleus, but also exists in mitochondria.
Purpose of the Study:
- To investigate the function of a truncated FEN1 isoform in mitochondria.
- To determine the substrate specificity and localization of the mitochondrial FEN1 isoform.
Main Methods:
- Alternative translation initiation analysis
- Mitochondrial import assays
- Immunocytochemistry and subcellular fractionation
- In vitro binding assays with various DNA/RNA structures
- Analysis of FENMIT's role in mitochondrial DNA replication under ethidium bromide treatment
Main Results:
- A truncated FEN1 isoform, FENMIT, is generated via alternative translation and targets mitochondria.
- FENMIT binds to RNA/DNA hybrids and R-loops, preferring 5' RNA flaps.
- FENMIT is recruited to mitochondrial DNA replication origins containing RNA/DNA hybrids and inhibits replication upon overexpression.
Conclusions:
- FENMIT is a mitochondrially localized FEN1 isoform with a role in processing RNA/DNA hybrids at the mitochondrial DNA replication origin.
- FENMIT may play a regulatory role in mitochondrial DNA replication by interacting with RNA/DNA structures.
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