A temperature sensitive Reca protein of Escherichia coli

The temperature sensitive allele recA200 has been cloned into the multiple copy number plasmid pBR322 and the gene product isolated. The purified RecA200 protein is temperature sensitive in ability to cleave the phage lambda and LexA repressors in vitro and also in ability to promote a successful search for homology between single stranded DNA and a homologous duplex leading to D-loop formation. However, at the non-permissive temperature the RecA200 protein has approximately wild type single stranded DNA dependent ATPase activity and ability to promote pairing between homologous single DNA strands. The demonstration that the temperature sensitivity in vivo can be correlated with the temperature sensitive cleavage of the lambda and LexA repressors in vitro and also with D-loop formation shows that these in vitro reactions, which require large amounts of RecA protein, are not carried out by trace amounts of contaminating proteins.