Molecular Cloning has significantly advanced the study of biology by allowing researchers to create recombinant proteins. Recombinant proteins are made by fusing genes (or parts of genes) from various organisms together in order to conduct functional studies using those very same "fusion proteins."
To generate these fusion proteins researchers commonly use restriction enzymes that recognize specific sites to cut (or digest) double stranded DNA and generate overhangs. The overhang generated depends on the enzyme used as well as its recognition site (see image below).
Once the proper overhangs are generated, what must a researcher do next, and which basic principle of DNA structure makes it possible?