Poster: Comparative Genomics

Abs # 917: Identification and characterization of a mitochondrial targeted RecA homologue in Arabidopsis thaliana

Presenter:	Nielsen, Brent L., brent_nielsen@byu.edu
Authors	Nielsen, Brent L. (A)   Edmondson, Andrew C (A)   Khazi, Fayaz R (B) (C)
Affiliations:	(A): Brigham Young University (B): The Childrens Hospital of Philadelphia (C): Auburn University

Homologous recombination occurs in essentially all organisms. RecA is the central enzyme involved in homologous DNA strand transfer. RecA is highly conserved in bacteria and has homologues in eukaryotes. While DNA recombination has been studied extensively in bacteria and nuclei of plants and other eukaryotes, there is very little information about this activity in plant mitochondria. Higher plant mitochondrial genomes contain repeated sequences that are known to undergo frequent rearrangements, but very little is known about the proteins involved or the biochemical mechanisms of DNA recombination in plant mitochondria. In searching the database we identified four E. coli RecA homologues in Arabidopsis thaliana. Only one of these (mtRecA) had a putative mitochondrial targeting sequence. The predicted presequence fused to the GFP coding sequence showed specific targeting of the fusion protein to purified mitochondria and not chloroplasts. Mitochondrial localization of the gene product was confirmed in western blots using an antibody against a unique 16 amino acid sequence from the N-terminal end of mtRecA. The nuclear gene (mtrecA) encodes a predicted gene product that shares highest sequence homology with chloroplast RecA and RecA proteins from the alpha subdivision of proteobacteria. Over-expression of Arabidopsis mtrecA in E. coli was confirmed by western analysis. Expression of mtrecA partially complemented a recA deletion in E. coli, suggesting a possible role in homologous mtDNA recombination and/or repair. A gene encoding a predicted mitochondrial targeted single-stranded DNA binding protein (mtSSB), which may be involved in mtDNA recombination as it is in E. coli, has been identified and is currently under investigation. This work is supported by the NIH.