Effect of internal direct and inverted Alu repeat sequences on PCR

Area of Science:

• Molecular Biology
• Genetics

Background:

• Alu repeats are abundant, ~300 bp long repetitive DNA sequences interspersed throughout the human genome.
• Understanding the behavior of repetitive DNA during molecular biology techniques like PCR is crucial for accurate genetic analysis.

Purpose of the Study:

• To investigate the impact of Alu repeats on polymerase chain reaction (PCR) amplification.
• To elucidate the mechanism behind PCR artifacts induced by repetitive DNA elements.

Main Methods:

• PCR amplification of the human low-density lipoprotein receptor gene containing two similarly oriented Alu repeats (~7.8 kb apart).
• PCR amplification of the human alpha-galactosidase A gene containing two nearby, inverted Alu repeats.
• Analysis of PCR products to identify deletions and assess the influence of template concentration and polymerase type.

Main Results:

• PCR amplification of the low-density lipoprotein receptor gene predominantly yielded a product with an in vitro deletion between the two distant, same-orientation Alu repeats.
• This deletion artifact formation was dependent on template concentration and polymerase choice, suggesting a "jumping reaction" mechanism.
• No such jumping products were observed when amplifying a region with nearby, inverted Alu repeats in the alpha-galactosidase A gene.

Conclusions:

• Distant, same-orientation Alu repeats can promote PCR artifacts, specifically in vitro deletions, via a primer-dimerization-like "jumping reaction".
• The orientation and proximity of repetitive elements significantly influence their potential to cause PCR artifacts.
• These findings highlight the challenges repetitive DNA poses for PCR-based genetic studies and emphasize the need for careful assay design.