The SOS response

If E. coli suffers severe DNA damage it activates the expression of a large number of diverse unlinked genes involved in DNA repair. All genes and operons under SOS control are subject to repression by the LexA protein. LexA has two domains – a dimerization and a DNA-binding domain. There is a conserved binding site known as a 'LexA box' located within the promoter of genes regulated by LexA.