English: The image depicts the three main stages of an OE-PCR assemby reaction. First, individual DNA sequences are amplified by PCR from different templates and flanked with the required complementary overhangs. Second, the formerly obtained PCR products are combined together into the overlap extension PCR reaction, where the complementary overhangs bind to each other allowing the polymerase to extend the DNA strand. Eventually, outer primers targeting the external overhangs are used and the desired DNA product is amplified in the final PCR reaction.