In vitro rapid synthesis of medium- and high-copy DNA repeats based on blocking polymerase chain reaction

A kit for synthesizing a DNA sequence comprising repeat units, the kit comprising a PCR reaction system,

• wherein the PCR reaction system comprises a single repeat unit of the repeat units, an extension primer and a blocking primer, wherein
• the extension primer consists of:
• from its 3′ end to its 5′ end, a sequence consisting of n nucleotides, the blocking primer, and the sequence consisting of n nucleotides, wherein n is an integer between 3 and 20;
• the single repeat unit of the repeat units consists of:
• from its 5′ end to its 3′ end, a nucleotide sequence fully complementary to the blocking primer and a nucleotide sequence fully complementary to the sequence consisting of n nucleotides
• wherein, when the 3′ end of the extension primer is connected in tandem to the 5′ end of the blocking primer, a connected product formed by the extension primer and the blocking primer consists of a sequence fully complementary to two of the repeat units;
• wherein the PCR reaction system further comprises polyethylene glycol (PEG), the PEG has a molecular weight between 2,000 Da and 20,000 Da, and the PEG has a concentration from 4 wt % to 20 wt % in the PCR reaction system;
• and
• wherein the PCR reaction system further comprises NaCl, with a concentration from 20 mM to 60 mM.