Linker element and method of using same to construct sequencing library

A method for constructing a sequencing library which uses a linker element consisting of a linker A and a linker B, wherein the linker A is generated from the complementary pairing of a long strand of nucleic acid and a short strand of nucleic acid, wherein the long strand has a phosphate modification at the 5′ end and the short strand has a blocking modification at the 3′ end, and has an enzyme active site in the short strand;

• and the linker B is a single-stranded nucleic acid, and the 3′ end thereof can be complementary to the 5′ end of the long strand of the linker A but the rest part cannot be complementary to the linker A,
• wherein the method comprises the steps of:
• (1) fragmenting a DNA to be tested;
• (2) dephosphorylating and blunt-end repairing the DNA fragments obtained in step 1);
• (3) linker ligations:
• linker A ligation:
• the linker A is added to both ends of the DNA fragments obtained in Step (2) by a ligation reaction;
• enzyme treatment and phosphorylation:
• depending on the enzyme active site in the short strand of the A linker, the DNA fragments ligated with the linker A are treated with the corresponding enzyme, and the unlinked 5′ ends of the fragments are phosphorylated;
• and
• linker B ligation:
• through a ligation reaction, the linker B is added to both ends of the DNA fragments ligated with the linker A;
• and
• (4) amplification of DNA fragments:
• polymerase chain reaction is carried out using the DNA fragments obtained in Step (3) as a template and using single-stranded nucleic acids C and D, which are complementary to the long strand of the linker A and the nucleic acid strand of the linker B, as primers,
• upon which steps the sequencing library is obtained.