"e. coli" strains deficient in reca are useful for cloning procedures in molecular biology laboratories. "e. coli" strains are often genetically modified to contain a mutant "reca" allele and thereby ensure the stability of extrachromosomal segments of dna, known as plasmids. in a process called transformation, plasmid dna is taken up by the bacteria under a variety of conditions. bacteria containing exogenous plasmids are called "transformants". transformants retain the plasmid throughout cell divisions such that it can be recovered and used in other applications. without functional reca protein, the exogenous plasmid dna is left unaltered by the bacteria. purification of this plasmid from bacterial cultures can then allow high-fidelity pcr amplification of the original plasmid sequence.