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. Author manuscript; available in PMC: 2017 Jul 1.
Published in final edited form as: Environ Mol Mutagen. 2016 Jun 7;57(6):421–434. doi: 10.1002/em.22023

Fig. 2.

Fig. 2

Induction of the SOS response in E. coli. The LexA repressor (green box) binds to a 20 base pair consensus sequence in the operator region of the SOS genes suppressing their expression. Upon UV irradiation, expression of RecA (red spheres) is induced after DNA damage occurs. RecA forms a nucleoprotein filament on ssDNA (RecA*) and functions as a coprotease to cleave and thereby inactivate the LexA repressor. The umuDC operon is fully derepressed ~15 min after DNA damage, however, due to rapid proteolysis of the Umu proteins, the UmuD'2C complexes themselves do not accumulate until ~ 45 min after damage. RecA* facilitates cleavage of UmuD (15 kDa) to UmuD' (12 kDa) removing the first 24 aa from the N–terminus of UmuD. Two molecules of UmuD' (UmuD'2) form a physical complex with UmuC (48kDa) forming pol V (72 kDa).