Hierarchical ligation-independent assembly of PCR fragments

The emerging field of synthetic biology requires novel cloning techniques that allow the rapid assembly of multiple expression units to build artificial genetic circuits. Here, we describe a rapid, flexible, and cost-efficient cloning method that requires only standard laboratory equipment and skills. Our technique relies on the 3'-5' exonuclease activity of T4 DNA polymerase to generate 20 nt single-stranded DNA overhangs that allow annealing and ligation-independent cloning (LIC) of four DNA fragments in one tube. The resulting intermediate-size constructs can be reused to hierarchically assemble constructs of more than 24 kb by the same method.