Biochemistry

Homologous Recombination

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Science  11 Oct 2013:
Vol. 342, Issue 6155, pp. 165
DOI: 10.1126/science.342.6155.165-a

In the 1970s, we learned that eukaryotic DNA contains introns—segments that are removed from RNA transcripts by splicing to yield messenger RNA. Since then, introns have been shown to play roles in regulating gene expression. In the 1990s came another surprise, that some proteins contain intervening sequences—inteins, which posttranslationally excise themselves and religate the remnants. Protein splicing usually occurs intramolecularly (cis), with the product comprising two elements (exteins) that were separated by the intein. However, in cyanobacteria, protein splicing also occurs between (trans) two monomer precursors, each containing parts of an intein and an extein. Association of the two monomers completes the intein, and the splicing reaction joins the two exteins. Aranko et al. found that splicing can occur between a cis-splicing precursor and a trans-splicing precursor, yielding up to four distinct ligation products. Expressing cis-splicing inteins with an artificially created C-terminal split intein fragment resulted in alternative splicing for all inteins tested, though the ratio of cis to alternative splicing varied. NMR spectroscopy and crystallography confirmed that the alternative splicing occurred through intermolecular domain swapping of inteins.

Nat. Chem. Biol. 9, 616 (2013).

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