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Proc Natl Acad Sci U S A. 1997 Aug 19;94(17):8994-9.

A protein encoded by a group I intron in Aspergillus nidulans directly assists RNA splicing and is a DNA endonuclease.

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Department of Biology, Temple University, Philadelphia, PA 19122, USA.

Erratum in

  • Proc Natl Acad Sci U S A 1997 Dec 23;94(26):14976.


Some group I introns self-splice in vitro, but almost all are thought to be assisted by proteins in vivo. Mutational analysis has shown that the splicing of certain group I introns depends upon a maturase protein encoded by the intron itself. However the effect of a protein on splicing can be indirect. We now provide evidence that a mitochondrial intron-encoded protein from Aspergillus nidulans directly facilitates splicing in vitro. This demonstrates that a maturase is an RNA splicing protein. The protein-assisted reaction is as fast as that of any other known group I intron. Interestingly the protein is also a DNA endonuclease, an activity required for intron mobilization. Mobile elements frequently encode proteins that promote their propagation. Intron-encoded proteins that also assist RNA splicing would facilitate both the transposition and horizontal transmission of introns.

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