The invention is directed to a method for obtaining a
nucleic acid library of a sample comprising polynucleotides comprising the steps: a. Providing a plurality of modified primer to the polynucleotides, wherein said modified primer is a starting point for a
polymerase for
nucleic acid amplification b. Amplification of the polynucleotides using a
polymerase c. Fragmentation of amplified polynucleotides, thereby obtaining a mixture of fragmented and un-fragmented polynucleotides comprising said modified primer d.
Ligation of a plurality of adapter oligonucleotides to the mixture obtained in step c), thereby obtaining a mixture of polynucleotides comprising said adapter oligonucleotides, wherein said adapter oligonucleotides comprise a
binding site for an amplification primer e. Providing an amplification primer to the mixture obtained in step d), wherein said amplification primer is a starting point for a
polymerase for
nucleic acid amplification f. initiate a nucleic acid amplification by providing a polymerase Characterized in that the modified primer provided in step a) comprises a functional group # wherein said functional group is a blocking group at the 5′ end of said modified primer, thereby preventing the
ligation of the adapter oligonucleotides or # wherein said functional group is at least one
nucleotide analogue, and wherein the
nucleotide analogue is excised after step d) by an
endonuclease, thereby removing the
primer binding site provided by the adapter oligonucleotides, thereby preventing binding of the amplification primer provided in step f) and a nucleic acid amplification of fragmented polynucleotides comprising the modified primer