Degenerate DNA recognition by I-PpoI endonuclease

Area of Science:

• Molecular Biology
• Enzymology
• Genetics

Background:

• The I-PpoI endonuclease, encoded by a group I intron in Physarum polycephalum, performs double-stranded DNA breaks at a specific 15-bp recognition site to facilitate intron homing.
• Homing endonucleases, including I-PpoI, are known for high substrate specificity, making them useful for genomic applications like mapping and sequencing.

Purpose of the Study:

• To investigate the cleavage activity of I-PpoI on recognition sites containing various mutations.
• To determine the extent of sequence degeneracy tolerated by I-PpoI and the impact of insertions/deletions and flanking regions on its catalytic function.

Main Methods:

• Analysis of I-PpoI endonuclease activity on engineered recognition sites with random and deliberate mutations.
• Assessment of cleavage efficiency in response to single and multiple nucleotide substitutions, deletions, and insertions within the target sequence.
• Evaluation of the influence of flanking DNA sequences on I-PpoI catalysis.

Main Results:

• I-PpoI exhibits significant tolerance for degeneracy within its 15-bp recognition site, with many single and multiple substitutions not preventing cleavage.
• Deletions or insertions within the recognition site severely impair I-PpoI's catalytic activity, highlighting the importance of precise substrate registry.
• The sequence context of the flanking regions was found to modulate I-PpoI's catalytic efficiency.

Conclusions:

• The I-PpoI endonuclease demonstrates a broader substrate recognition profile than previously assumed, accommodating substantial sequence variation.
• I-PpoI combines the sequence-specific binding characteristics of transcription factors with the catalytic precision of restriction endonucleases.
• The enzyme's adaptability suggests potential for refined applications in genome engineering and manipulation.