piggyBac can bypass DNA synthesis during cut and paste transposition

Area of Science:

• Molecular Biology
• Genetics
• Genomics

Background:

• Transposable elements (TEs) are mobile DNA sequences crucial for genome evolution.
• DNA synthesis was thought to be essential for TE transposition, particularly for DNA transposons like piggyBac.
• The piggyBac transposon is a valuable tool for genome engineering across diverse organisms, including mammals.

Purpose of the Study:

• To elucidate the precise molecular mechanism of piggyBac transposition.
• To determine if DNA synthesis is a mandatory step in piggyBac excision and integration.
• To classify the piggyBac transposase within known superfamilies of recombinases.

Main Methods:

• Established a novel piggyBac transposition system in Saccharomyces cerevisiae for in vitro and in vivo analysis.
• Investigated transposon excision by analyzing donor site repair intermediates.
• Studied transposon integration by characterizing target DNA modifications and utilizing mutant transposases.

Main Results:

• Demonstrated that DNA synthesis is dispensable for both piggyBac transposon excision and integration.
• Revealed that piggyBac excision proceeds through transient hairpin formation at transposon ends.
• Showed that piggyBac integration involves direct nucleophilic attack by the transposon's 3' hydroxyl ends onto target DNA.
• Identified piggyBac transposase as a member of the DDE superfamily of recombinases, despite lacking sequence homology.

Conclusions:

• PiggyBac transposition bypasses the need for DNA synthesis, utilizing a mechanism distinct from previously characterized DNA transposons.
• The direct attack mechanism for integration is conserved among DDE superfamily transposases and retroviral integrases.
• The classification of piggyBac transposase within the DDE superfamily provides new insights into TE evolution and mechanism.