text: In recursive directional ligation, the gene encoding the monomer is inserted into a plasmid with restriction sites that are recognized by at least two endonucleases. The endonucleases will cut the plasmid, releasing the gene of interest. Then, this single gene is inserted into a recipient plasmid vector already containing one copy of the ELP monomer gene via digestion of the recipient plasmid with the same restriction endonucleases used on the donor plasmid and a subsequent ligation step.  From this process, a sequence of two ELP monomer genes is retrieved.  RDL allows for the controlled synthesis of ELP gene oligomers, in which single gene segments are sequentially added.  However, the restriction endonucleases used are limited to those that do not cut within the ELP monomer gene itself, as this would lead to loss of crucial nucleotides and a potential frameshift mutation in the protein.