A method of producing an asymmetrically tagged nucleic acid fragment, said method comprising the steps: i. ligating a first adapter nucleic acid molecule to a template strand of a double-stranded nucleic acid fragment and a second adapter nucleic acid molecule to a complementary strand of said double-stranded nucleic acid fragment, wherein said first and said second adapter nucleic acid molecule are characterized by an identical base sequence and comprise a ligation site and a primer-binding region, and said primer-binding region comprises a. at least one universal base and/or b. at least one convertible base, and wherein optionally said first adapter nucleic acid molecule and said second adapter nucleic acid molecule are double-stranded, and wherein optionally both strands of said first and said second adapter nucleic acid molecule are ligated to said double-stranded nucleic acid fragment; ii. optionally converting said at least one convertible base comprised within said first and/or said second adapter nucleic acid molecule into an at least one converted base; iii. obtaining a first antisense adapter and a second antisense adapter by performing a first extension step, wherein a. said complementary strand is extended yielding said first antisense adapter ligated to said complementary strand, and said template strand is extended yielding a second antisense adapter ligated to said template strand, or b. a primer is annealed to a strand of said second adapter nucleic acid molecule ligated to said template strand and extended yielding a nucleic acid strand comprising said primer, a nucleic acid sequence complementary to said template strand, and said first antisense adapter, and a primer is annealed to a strand of said first adapter nucleic acid molecule ligated to said complementary strand and extended yielding a nucleic acid strand comprising said primer, a nucleic acid sequence complementary to said complementary strand, and said second antisense adapter, wherein said first antisense adapter is complementary to said first adapter nucleic acid molecule and said second antisense adapter is complementary to said second adapter nucleic acid molecule except at positions opposite to said at least one universal, convertible or converted base comprised within said first and second adapter nucleic acid molecule, thereby yielding an asymmetrically tagged nucleic acid fragment. i. ligating a first adapter nucleic acid molecule to a template strand of a double-stranded nucleic acid fragment and a second adapter nucleic acid molecule to a complementary strand of said double-stranded nucleic acid fragment, wherein said first and said second adapter nucleic acid molecule are characterized by an identical base sequence and comprise a ligation site and a primer-binding region, and said primer-binding region comprises a. at least one universal base and/or b. at least one convertible base, and wherein optionally said first adapter nucleic acid molecule and said second adapter nucleic acid molecule are double-stranded, and wherein optionally both strands of said first and said second adapter nucleic acid molecule are ligated to said double-stranded nucleic acid fragment; a. at least one universal base and/or b. at least one convertible base, ii. optionally converting said at least one convertible base comprised within said first and/or said second adapter nucleic acid molecule into an at least one converted base; iii. obtaining a first antisense adapter and a second antisense adapter by performing a first extension step, wherein a. said complementary strand is extended yielding said first antisense adapter ligated to said complementary strand, and said template strand is extended yielding a second antisense adapter ligated to said template strand, or b. a primer is annealed to a strand of said second adapter nucleic acid molecule ligated to said template strand and extended yielding a nucleic acid strand comprising said primer, a nucleic acid sequence complementary to said template strand, and said first antisense adapter, and a primer is annealed to a strand of said first adapter nucleic acid molecule ligated to said complementary strand and extended yielding a nucleic acid strand comprising said primer, a nucleic acid sequence complementary to said complementary strand, and said second antisense adapter, wherein said first antisense adapter is complementary to said first adapter nucleic acid molecule and said second antisense adapter is complementary to said second adapter nucleic acid molecule except at positions opposite to said at least one universal, convertible or converted base comprised within said first and second adapter nucleic acid molecule, thereby yielding an asymmetrically tagged nucleic acid fragment. a. said complementary strand is extended yielding said first antisense adapter ligated to said complementary strand, and said template strand is extended yielding a second antisense adapter ligated to said template strand, or b. a primer is annealed to a strand of said second adapter nucleic acid molecule ligated to said template strand and extended yielding a nucleic acid strand comprising said primer, a nucleic acid sequence complementary to said template strand, and said first antisense adapter, and