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A site-specific endonuclease encoded by a typical archaeal intron
J Z Dalgaard1, R A Garrett, M Belfort
1Molecular Genetics Program, Wadsworth Center for Laboratories, New York State Department of Health, Albany 12201-0509.
Summary
The archaeal intron protein I-Dmo I from Desulfurococcus mobilis is a thermostable double-strand DNase. It shares sequence similarity with eukaryotic group I intron endonucleases, suggesting independent evolution.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- Archaeal introns, specifically within the 23S rRNA gene of hyperthermophiles like Desulfurococcus mobilis, encode unique proteins.
- Homing endonucleases are enzymes involved in intron mobility and gene targeting, often found in various intron types.
Purpose of the Study:
- To characterize the double-strand DNase encoded by the archaeal intron in Desulfurococcus mobilis.
- To investigate the properties and evolutionary relationships of this archaeal intron-encoded endonuclease, named I-Dmo I.
Main Methods:
- Biochemical characterization of the I-Dmo I enzyme.
- Comparative sequence analysis with known intron endonucleases.
- Analysis of enzyme expression from different intron species (linear, cyclized, precursor RNA).
Main Results:
- I-Dmo I is a thermostable double-strand DNase capable of cleaving intronless alleles.
- It exhibits a staggered double-strand cut generating 4-nt 3' extensions, similar to eukaryotic counterparts.
- I-Dmo I shares the LAGLI-DADG motif with eukaryotic group I intron endonucleases despite differing intron structures and splicing pathways.
Conclusions:
- The findings support the independent evolutionary origin of archaeal endonucleases and intron core elements.
- The presence of conserved motifs suggests functional convergence or horizontal gene transfer.
- Endonuclease genes possess invasive potential, contributing to intron propagation.