Multiple homing pathways used by yeast mitochondrial group II introns

Area of Science:

• Molecular Biology
• Genetics
• Retrotransposition

Background:

• Group II introns are mobile genetic elements found in various organisms, including yeast.
• Intron homing is a process where introns insert into specific DNA sites, often involving reverse transcriptase activity.

Purpose of the Study:

• To investigate the distinct homing pathways of yeast mitochondrial DNA group II introns aI1 and aI2.
• To differentiate between reverse transcriptase (RT)-dependent (retrohoming) and RT-independent homing mechanisms.
• To analyze the role of flanking marker coconversion patterns in elucidating these pathways.

Main Methods:

• Utilized genetic crosses with wild-type and mutant aI2 introns in yeast.
• Analyzed patterns of flanking marker coconversion to distinguish homing pathways.
• Investigated RT-dependent and RT-independent mechanisms initiated by endonuclease cleavage.

Main Results:

• Identified three distinct homing pathways: two RT-dependent (retrohoming) and one RT-independent.
• The major retrohoming pathway involves target DNA-primed reverse transcription and double-strand break repair (DSBR).
• A novel RT-independent pathway, observed with mutant target sites, bypasses coconversion and homologous recombination.

Conclusions:

• Yeast group II intron mobility is highly flexible, utilizing multiple distinct homing pathways.
• The prevalence of each pathway is determined by the specific intron and DNA target site characteristics.
• This flexibility allows group II introns to adapt and utilize diverse recombination and repair systems across different cellular environments.