Abstract: The invention relates to a method for synthesising long nucleic acids, including at least one cycle of elongating initial fragments of nucleic acids, including a) a phase comprising the enzymatic addition of nucleotides to said fragments, b) a phase comprising the purification of the fragments having a correct sequence, c) an optional phase of enzymatic amplification, each cycle being performed in a reaction medium which is compatible with enzymatic addition and amplification, such as an aqueous medium, the synthesis method also comprising, at the end of all the elongation cycles, a last step of final amplification. The invention also relates to the use of the method for the production of genes, or sequences of synthetic nucleic acids, DNA or RNA. The invention further relates to a kit for implementing said method.

Abstract: The present invention relates to variants of Terminal deoxynucleotidyl Transferase (TdT), each of which (i) has an amino acid sequence similarity to SEQ ID NO: 2. 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31, 33 or 35 with corresponding amino acid substitutions, (ii) is capable of synthesizing a nucleic acid fragment without a template and (iii) is capable of incorporating a modified nucleotide into the nucleic acid fragment.