What level of purity is required for dNTPs used in cloning sequencing?

The supply of 100 mM dNTPs from several mainstream imported brands is generally stable, but there may be differences in concentration and packaging specifications. 100 mM is a commonly used concentration, and 250 μ L/tube is often in stock. Large packages such as 1 mL/5 mL may require adjustment. Our laboratory uses 2-3 mL per month, and I will place an order one month in advance, asking the supplier to write the delivery date and batch number in the contract, and requiring the same batch number to cover at least one complete project to avoid introducing variables during batch changes. After arrival, check the purity on the CoA first pH、 The endotoxin and nuclease indicators are then divided into working solutions. If the import delivery time is unstable, it is also possible to consider domestic agents with spot goods or domestically produced HPLC grade products. However, before officially using them for cloning sequencing, small sample parallel validation should be done first, and do not directly switch brands for large quantities.

After switching to HPLC dNTPs, it is recommended to perform a systematic verification: using the same high-fidelity enzyme, the same primers and template, amplify a 1.5 kb fragment separately, purify it, and then perform blunt-end ligation. Pick 8–24 clones per condition for sequencing, and tally the mutation types and positions. If mutations mainly occur at the same position, the issue may not be the dNTPs but rather primer mismatch or heterogeneity in the template itself; if they are randomly scattered, then focus on checking the dNTPs and enzyme. At the same time, you can ask the supplier to provide the HPLC purity and DNase/RNase testing reports for that lot, and if necessary, measure the A260/A280 ratio yourself. In addition, before blunt-end cloning, it is best to perform end phosphorylation and purification to avoid extraneous peaks at the ends of the PCR product interfering with ligation. This is more reliable than simply guessing.

For flat end cloning and sequencing, I would recommend at least using HPLC to purify dNTPs. Ordinary dNTPs may retain small amounts of other dNTPs, modified nucleotides, or metal ions, leading to polymerase misdoping or incomplete end repair, resulting in individual mutations after cloning. The 1.5kb fragment is not considered long, but flat end cloning requires higher end integrity and fidelity than TA cloning, and HPLC purification can reduce impurity interference. However, mutations are not necessarily the sole responsibility of dNTPs, as high fidelity enzymes, primer purity, excessive cycle numbers, and template damage can all introduce mutations. You can first change the HPLC dNTPs and reduce the number of cycles to 25-28. At the same time, use the same template to do three parallel clone sequencing to see whether the mutation rate has decreased, and then judge whether to change the enzyme or optimize the conditions.

Imported brands of 100 mM dNTPs vary significantly in price. Common single-vial sizes are 25 μL, 100 μL, and 250 μL, and some are priced per μmol. Converted to per mL, the cost is usually in the high hundreds to over one thousand RMB, while some brands or promotional channels may be lower; the exact price is subject to the agent's formal quotation. You use 2–3 mL per month, which is not a small amount. It is advisable to ask the agent directly for a quotation on 5 mL or 10 mL bulk packaging, as the cost per mL is usually lower. Imported brands have stable supply, but 100 mM bulk packaging is not necessarily kept in regular stock, and the lead time may be 2–4 weeks, so safety stock should be prepared in advance. You can also ask two agents at the same time and compare the total price, shelf life, and whether cold-chain shipping is included. Do not look only at the unit price; bulk packaging with a short shelf life may go to waste if it cannot be used up.