Structures of vertebrate R2 retrotransposon complexes during target-primed reverse transcription and after...

Area of Science:

• Molecular Biology
• Genetics
• Structural Biology

Background:

• R2 retrotransposons are non-long terminal repeat elements that insert into ribosomal RNA genes.
• Avian A-clade R2 proteins can efficiently and precisely insert transgenes into safe-harbor loci in human cells.
• The structural features enabling this precise gene insertion by A-clade R2 proteins are not well understood.

Purpose of the Study:

• To elucidate the structural basis for the high selectivity and efficiency of vertebrate A-clade R2 proteins in gene insertion.
• To characterize the roles of individual zinc-finger domains in nucleic acid recognition.
• To provide structural insights into the mechanism of target-primed reverse transcription and gene insertion.

Main Methods:

• High-resolution cryo-electron microscopy (cryo-EM) of two vertebrate A-clade R2 proteins.
• Biochemical assays to assess nucleic acid binding and enzymatic activity.
• Cellular assays to evaluate gene insertion efficiency and specificity.

Main Results:

• Determined cryo-EM structures of R2 proteins at key stages of reverse transcription and DNA modification.
• Identified specific roles for the three zinc-finger domains in template and target recognition.
• Discovered an insertion motif within the reverse transcriptase active site unique to vertebrate A-clade R2 proteins that enhances structural integrity.

Conclusions:

• The study provides the first structural insights into the mechanism of gene insertion by vertebrate A-clade R2 proteins.
• Understanding these structural features can guide the development of R2-based systems for precise transgene insertion.
• These findings pave the way for improved gene editing and gene therapy tools.