What are the common PCR additives?

PCR additives are used to reduce complex secondary structures, which in turn increases amplification of target DNA and improves the yields of hard to amplify products such as GC-rich templates. Each PCR additive works using a different mechanism. 

Common PCR additives include: 

Dimethyl Sulfoxide (DMSO) 

DMSO is often recommended when amplifying GC rich templates as it reduces secondary DNA structures. However, it also interferes with and reduces the activity of Taq polymerase. To get the best results, it’s advisable to test multiple DMSO concentrations between 2% and 10% in order to strike a balance between template accessibility and Taq activity. 

Betaine

Betaine enhances DNA amplification and specificity by reducing the formation of secondary structures and eliminating the base pair composition dependence of DNA melting. 

Formamide

A widely used organic PCR additive, formamide is thought to work by lowering the melting temperature, destabilizing the template double-helix and binding in the major and minor grooves of DNA. It is generally used at 1-5%.

Tetramethylammonium chloride (TMAC)

TMAC is the preferred additive in PCR conditions that use degenerate primers. It eliminates non-specific priming and potential mismatch between DNA and RNA by increasing melting temperature and enhancing hybridization specificity. 

Magnesium

Magnesium is an essential cofactor for Taq polymerase, which is inactive without the adequate amount of free magnesium. Magnesium concentrations must be tested in intervals to find the ideal concentration for your specific reaction as excess magnesium can compromise Taq fidelity. 

Bovine serum albumin (BSA) 

BSA is a common PCR additive. It works by suppressing contaminants such as phenolic compounds and by preventing components of the reaction from adhering to tube walls. 

Non-ionic detergents

Tween 20, NP-40 and Triton X-100 are some of the more common non-ionic detergents used as PCR additives. Non-ionic detergents reduce secondary structures, resulting in clean, low-yield PCRs. The downside is they increase non-specific amplification and must be used with caution in dirty PCR reactions.