TREATMENT OF PEA (PISUM-SATIVUM L) PROTOPLASTS WITH DNA-DAMAGING AGENTS INDUCES A 39-KILODALTON CHLOROPLAST PROTEIN IMMUNOLOGICALLY RELATEDTO ESCHERICHIA-COLI RECA

Organisms must have efficient mechanisms of DNA repair and recombinati on to prevent alterations in their genetic information due to DNA dama ge. There is evidence for DNA repair and recombination in plastids of higher plants, although very little is known at the biochemical level. Many chloroplast proteins are of eubacterial ancestry, suggesting tha t the same could be true for the components of a DNA repair and recomb ination system. A 39-kD protein, immunologically related to Escherichi a coli RecA, is present in chloroplasts of pea (Pisum sativum L.). Ban dshift gel assays suggest that it binds single-stranded DNA. Its stead y-state level is increased by several DNA-damaging agents. These resul ts are consistent with it being a plastid homolog of E. coli RecA prot ein, presumably involved in DNA repair and recombination, and with the existence of an SOS-like response in pea leaf cells. Experiments with protein synthesis inhibitors suggest that the 39-kD chloroplast prote in is encoded in the nucleus.