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Recombinase IS621 Bias The IS621 recombinase, which rearranges DNA, inserts segments 2,000 times more frequently than it excises. An article published on August 12 in Nature explored why the IS621 recombinase is more efficient at inserting DNA segments than excising them. The authors linked this bias to the shape of the complex formed by the protein, RNA, and DNA, and increased the excision frequency in E. coli bacterial plasmids by modifying the guide RNA. The IS621 is a mobile DNA fragment from the IS110 family, which encodes a recombinase that first excises the fragment from DNA, forming a circular double-stranded molecule, and then inserts it into a new location. A 2024 study showed that these addresses can be changed; the new article explains why the reverse step is much less efficient. Experiments with purified protein, defined DNA segments, and constructed bridge RNA showed that excision yielded 0.03% product, while insertion yielded 63%. Labels on the DNA allowed researchers to see where efficiency was lost: after the first cut in both cases, intermediate molecules accumulated, but the next step - the exchange of cut DNA strands - proceeded much worse for excision. 🔗 Read original →