Method for producing circular DNA formed from single-molecule DNA

An adapter for producing a circular DNA, the adapter consisting of two DNA strands complementary to each other having the following structure y1-Y-y2-X:

• wherein
• X represents a double-stranded DNA being a restriction enzyme recognition site comprising a palindromic sequence;
• y1 and y2 represent double-stranded DNAs respectively comprising identical nick-generating enzyme recognition sites being reversely oriented to each other;
• Y represents a double-stranded DNA sequence having a unique sequence for each DNA molecule to be circularized, n represents an integer of 4 to 15, N1 to Nn, which may be the same or different, each represent a deoxyribonucleotide selected from the group consisting of dAMP, dCMP, dGMP and dTMP, and N′1 to N′n represent the following deoxyribonucleotides respectively corresponding to the N1 to Nn,
• TABLE 1
• Nk
• N′k
• dAMP
• dTMP
• dCMP
• dGMP
• dGMP
• dCMP
• dTMP
• dAMP
• wherein k represents an integer from 1 to n.