Yeast tRNA-splicing endonuclease cleaves precursor tRNA in a random pathway
The Journal of Biological Chemistry
|January 5, 1993
Summary
The tRNA endonuclease cleaves pre-tRNA introns independently at the 3' and 5' splice sites. While initial cleavage rates are similar, subsequent cleavage favors the 3' site, indicating a random intron removal process.
Area of Science:
- Molecular Biology
- Biochemistry
- Yeast Genetics
Background:
- Introns are non-coding sequences within precursor transfer RNA (pre-tRNA) genes in Saccharomyces cerevisiae.
- Accurate cleavage of pre-tRNA by tRNA endonuclease at specific splice sites is essential for intron removal and functional tRNA maturation.
Purpose of the Study:
- To investigate the order and kinetics of splice site cleavage by tRNA endonuclease.
- To determine if splice site cleavage is a coordinated or independent process.
Main Methods:
- Phosphorylation of ribose 2'-OH at splice sites to block endonuclease activity.
- Preparation and analysis of nicked pre-tRNA and intermediate "2/3 molecules".
- Kinetic studies comparing cleavage rates at 3' and 5' splice sites.
Main Results:
- Phosphorylation of either splice site blocked cleavage, but the other site remained accessible, demonstrating independent cleavage.
- tRNA endonuclease cleaved both 3'- and 5'-nicked pre-tRNA.
- Kinetic analysis revealed near-equal rates for initial 3' and 5' site cleavage, with faster 3' site cleavage in the second step.
- True biochemical intermediates ("2/3 molecules") were identified.
Conclusions:
- tRNA endonuclease cleaves pre-tRNA splice sites in a random order.
- Two distinct pathways exist for intron removal, with unequal rates for sequential cleavage steps.
- The findings elucidate the mechanism of intron excision in yeast pre-tRNA processing.
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