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John M. S. Bartlett.pdf - Bio-Nica.info

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472 Wang<br />

Fig. 1. A brief outline of the strategy used to generate sticky-end PCR products with T4<br />

DNA polymerase.<br />

methods can be used to purify DNA fragments from agarose gel, such as phenol extraction<br />

from low-melting gel (8), the “glassmilk” method, or simple low-speed centrifugation<br />

(10). The phenol extraction method has been found to be less expensive and able to recover<br />

a sufficient amount of clean DNA for cloning.<br />

2. This protocol uses one buffer for all the enzymes that include Taq polymerase in PCR,<br />

T4 polymerase, and T4 polynucleotide kinase in end-repair reaction. Therefore, a slightly<br />

higher concentration of reagents and enzymes can be added in the reaction.<br />

3. T4 DNA polymerase can be added directly into the PCR tube without providing additional<br />

nucleotides. However, T4 DNA polymerase balances its exonuclease and polymerase<br />

activities based on the concentration of available deoxynucleotides. Depending on the<br />

length of amplification products, number of amplification cycles, and nucleotide sequence<br />

composition of amplified region, the remaining nucleotide concentration after PCR<br />

amplification may be different from experiment to experiment. To avoid unnecessary<br />

confusion, supplemental nucleotides are routinely added for end-repair reaction.<br />

4. T4 polynucleotide kinase is not needed when vector used has not been treated with<br />

phosphatase previously. However, dephosphorylated vector should be used to increase<br />

the cloning efficiency.

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