Identification of the amino acid substitutions in two mutant forms of the recA protein from Escherichia coli: recA441 and recA629.

We have identified the amino acid substitutions in two mutant forms of the recA protein from Escherichia coli. The recA441 mutant, which shows constitutive expression of the recA-mediated SOS response at 42 degrees C, contains two amino acid substitutions, glutamic acid to lysine at residue 38 and isoleucine to valine at residue 298. The recA629 mutant is an unusual pseudorevertant of recA441 that is no longer capable of spontaneous expression of SOS functions at 42 degrees C. Purified recA629 protein is cold-labile for several of the wild-type enzymatic activities and is shown here to contain three amino acid substitutions, the two found in the recA441 protein at residues 38 and 298, as well as an aspartic acid-to-glycine change at residue 32. The mutation at residue 32 was verified by restriction digestion of the 5' region of the recA629 structural gene.