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A factor related to pseudouridine synthases is required for chloroplast group II intron trans-splicing in
K Perron1, M Goldschmidt-Clermont, J D Rochaix
1Departments of Molecular Biology and Plant Biology, University of Geneva, 30, Quai Ernest-Ansermet, 1211 Geneva, Switzerland.
Abstract:
In Chlamydomonas reinhardtii, the psaA mRNA is assembled by a process involving two steps of trans-splicing that remove two group II introns and give rise to the mature mRNA. The products of at least 14 nuclear genes and one chloroplast gene (tscA) are necessary for this process. We have cloned Maa2, one of the nuclear genes involved in trans-splicing of the second intron. Maa2 encodes a protein with similarity to conserved domains of pseudouridine synthases, but mutagenesis of putative catalytic residues showed that this activity may not be required for trans-splicing of psaA RNA. Although it is not clear whether the pseudouridine synthase activity has been maintained in Maa2, it is possible that this enzyme was recruited during evolution as an RNA chaperone for folding or stabilizing the psaA intron. The Maa2 protein appears to be associated through ionic interactions with a low density membrane system in the chloroplast that also contains RNA-binding proteins involved in translation.
Insights
Researchers identified Maa2, a nuclear gene crucial for assembling the psaA mRNA in Chlamydomonas reinhardtii. This gene
Area of Science:
- * Molecular Biology
- * Genetics
- * Biochemistry
Background:
- * The psaA mRNA in Chlamydomonas reinhardtii requires a two-step trans-splicing process to remove group II introns and form mature mRNA.
- * This essential process relies on products from at least 14 nuclear genes and one chloroplast gene (tscA).
Purpose of the Study:
- * To identify and characterize nuclear genes involved in the trans-splicing of the second intron of psaA mRNA.
- * To investigate the function and potential enzymatic activity of the cloned Maa2 gene product in RNA splicing.
Main Methods:
- * Gene cloning of Maa2 from Chlamydomonas reinhardtii.
- * Mutagenesis of putative catalytic residues within the Maa2 protein.
- * Biochemical association studies of the Maa2 protein within the chloroplast.
Main Results:
- * Maa2 was cloned and found to encode a protein with similarity to pseudouridine synthases.
- * Mutagenesis experiments indicated that the putative catalytic activity of pseudouridine synthase may not be essential for psaA RNA trans-splicing.
- * The Maa2 protein was found to associate with a chloroplast membrane system containing RNA-binding proteins.
Conclusions:
- * Maa2 is a nuclear gene product essential for psaA mRNA trans-splicing in Chlamydomonas reinhardtii.
- * While Maa2 shares similarity with pseudouridine synthases, its catalytic activity might not be its primary role in this splicing process.
- * Maa2 may function as an RNA chaperone, potentially aiding in intron folding or stabilization, and is localized within the chloroplast.