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Abstract Detail


Mechanisms of Gene Regulation

Fischer, Michael J. [1], Upchurch, Kyle M. [1], Higgs, David C. [2].

Characterization of 5'-3' Exoribonucleases in the green alga Chlamydomonas reinhardtii.

5'-3' exoribonucleases (Xrn's) are eukaryotic RNases that are important in RNA degradation and processing. In the green alga Chlamydomonas reinhardtii, a 5'-3' exoribonucleolytic activity exists in chloroplasts that is part of the normal degradation of some chloroplast mRNAs. Analysis of the completely sequenced C. reinhardtii chloroplast genome revealed no RNase genes. Thus, this chloroplast activity is most likely nucleus-encoded and the responsible RNase(s) post-translationally targeted to the chloroplast. Bioinformatic analysis of the C. reinhardtii nuclear genome (http://genome.jgi-psf.org/Chlre3) and ESTs, plus the probing of a BAC genomic library, helped us identify three candidate nuclear Xrn genes, termed CrXrn1, CrXrn2, and CrXrn3. We have confirmed expression of these genes at the RNA level, using RT-PCR and cDNA sequencing. Relevant to the chloroplast activity, CrXrn1 accumulates two alternatively spliced mRNAs (CrXrn1a and CrXrn1b). Southerns confirm the existence of only one gene with CrXrn1-specific sequence, supporting our alternative splicing model. We predict the CrXrn1a mRNA splice variant to encode a type I cytosolic Xrn. While the CrXrn1b mRNA splice variant is predicted to encode a type I Xrn with an N-terminal extension that has sequence and structural features very similar to known C. reinhardtii chloroplast transit peptides. We hypothesize that CrXrn1b is chloroplast targeted where it would provide the published 5’-3’ exoribonuclease activity. To date, an Xrn protein with an N-terminal extension has not been published. Further testing of these Xrn’s, alternative splicing, cellular location, and biological functions are in progress.


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1 - University of Wisconsin-Parkside, Biological Sciences
2 - University of Wisconsin-Parkside, Biological Sciences, 900 Wood Road, Kenosha, WI, 53141, USA

Keywords:
Transcript stability
Organelle
RNA splicing.

Presentation Type: Plant Biology Abstract
Session: P
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM
Number: P36056
Abstract ID:2355


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