The chloroplast-located homolog of bacterial DNA recombinase

Abstract

The cDNA for the chloroplast-located homolog of bacterial RecA protein, designated recA-AT, was placed in a plasmid appropriate for in vitro transcription and translation. Translation with 35S-labeled Met permitted demonstration of uptake of the protein product into isolated pea chloroplasts, and processing to a mature size. Preliminary evidence for the first amino acid was estimated from results using both 35S-Met and 3H-Leu for in vitro transcription and translation, followed by uptake into chloroplasts and processing. The labeled protein was subject to sequential amino acid hydrolyses, and radioactivity was measured in each round. Induction of gene transcription in leaves infiltrated with the DNA-damaging agent, methyl methane-sulfonate was shown by Northern blot analysis. Further constructs were made for over-expression of the gene in E. coli; and one out of many tried permitted production of some soluble protein. Extracts from transformed bacteria were shown to have RecA activity using the "POM" assay [Bertrand et al. (1993) Nucl. Acids Res. 21:3653] for DNA strand transfer. The protein was purified to close to homogeneity using methods developed for E. coli RecA isolation.