System for producing a nucleic acid construct of interest, said system comprising: a set of n entry DNAs numbered 1 to n, n being an integer of at least 2, preferably at least 3, each of said n entry DNAs comprising in this order: (i) a type IIs restriction endonuclease recognition site followed by the cleavage site thereof; (ii) a sequence portion linking the cleavage site of said recognition site of item (i) with the cleavage site of the recognition site of the following item (iii), and (iii) a cleavage site of a further type IIs restriction endonuclease recognition site followed by the recognition site of said cleavage site; the cleavage sites of the type IIs restriction endonuclease recognition site(s) of item (iii) of entry DNA(s) 1 to n-1 is/are complementary to the cleavage site(s) of the type IIs restriction endonuclease recognition site(s) of item (i) of entry DNA(s) 2 to n, respectively; the cleavage site of the type IIs restriction endonuclease recognition site of item (iii) of entry DNA n is complementary to the cleavage site of the type IIs restriction endonuclease recognition site of item (i) of entry DNA 1; said system further comprising a destination vector comprising in this order: a type IIs restriction endonuclease recognition site followed by the cleavage site thereof; a vector backbone comprising a selectable marker gene, said vector backbone linking the cleavage sites of said recognition sites of items and the following item; a further cleavage site of a type IIs restriction endonuclease recognition site followed by the recognition site of said cleavage site, and optionally, an insert between the recognition sites of item and item. a set of n entry DNAs numbered 1 to n, n being an integer of at least 2, preferably at least 3, each of said n entry DNAs comprising in this order: (i) a type IIs restriction endonuclease recognition site followed by the cleavage site thereof; (ii) a sequence portion linking the cleavage site of said recognition site of item (i) with the cleavage site of the recognition site of the following item (iii), and (iii) a cleavage site of a further type IIs restriction endonuclease recognition site followed by the recognition site of said cleavage site; (i) a type IIs restriction endonuclease recognition site followed by the cleavage site thereof; (ii) a sequence portion linking the cleavage site of said recognition site of item (i) with the cleavage site of the recognition site of the following item (iii), and (iii) a cleavage site of a further type IIs restriction endonuclease recognition site followed by the recognition site of said cleavage site; the cleavage sites of the type IIs restriction endonuclease recognition site(s) of item (iii) of entry DNA(s) 1 to n-1 is/are complementary to the cleavage site(s) of the type IIs restriction endonuclease recognition site(s) of item (i) of entry DNA(s) 2 to n, respectively; the cleavage site of the type IIs restriction endonuclease recognition site of item (iii) of entry DNA n is complementary to the cleavage site of the type IIs restriction endonuclease recognition site of item (i) of entry DNA 1; said system further comprising a destination vector comprising in this order: a type IIs restriction endonuclease recognition site followed by the cleavage site thereof; a vector backbone comprising a selectable marker gene, said vector backbone linking the cleavage sites of said recognition sites of items and the following item; a further cleavage site of a type IIs restriction endonuclease recognition site followed by the recognition site of said cleavage site, and optionally, an insert between the recognition sites of item and item. a type IIs restriction endonuclease recognition site followed by the cleavage site thereof; a vector backbone comprising a selectable marker gene, said vector backbone linking the cleavage sites of said recognition sites of items and the following item; a further cleavage site of a type IIs restriction endonuclease recognition site followed by the recognition site of said cleavage site, and optionally, an insert between the recognition sites of item and item.