Identification and expression analysis of cDNA encoding a chloroplast recombination protein REC1, the chloroplast RecA homologue in Chlamydomonas reinhardtii

Chloroplasts of plant cells have their own genome, and a basic recombination protein homologous to the eubacterial RecA was suggested to be involved in the perpetuation of chloroplast DNA. A candidate cDNA sequence encoding the chloroplast RecA protein was identified from the Kazusa EST database for the unicellular green alga, Chlamydomonas reinhardtii (http://www.kazusa.or.jp/en/plant/chlamy/EST/). Analysis of the cDNA sequence identified an open reading frame (ORF) of 414 amino acids encoding a eubacteria-type RecA protein. Thus the corresponding gene was named REC1. The predicted protein contains an N-terminal extension that does not show any similarity with other RecA proteins. Transient expression of a REC1-sGFP (green fluorescent protein) fusion construct in tobacco cells has indicated that this N-terminal sequence functions as a transit peptide for import into chloroplasts. Since DNA-damaging reagents induced the REC1 mRNA, REC1 was suggested to have roles in DNA recombination and repair of the chloroplast DNA in C. reinhardtii.