Inactivation of DNA proofreading obviates the need for SOS induction in frameshift mutagenesis

• DOI: 10.1073/pnas.95.22.13114
• Publication Date: 2002-07-26T14:35:50Z
• Authors: Robert P. P. Fuchs; Rita L. Napolitano
• Keywords: DNA Replication; 0301 basic medicine; Base Sequence; Models, Genetic; Ultraviolet Rays; Templates, Genetic; 2-Acetylaminofluorene; Cytosine; 03 medical and health sciences; Bacterial Proteins; Mutagenesis; Escherichia coli; Frameshift Mutation; SOS Response, Genetics; Plasmids

Translesion synthesis at replication-blocking lesions requires the induction of proteins that are controlled by the SOS system in Escherichia coli . Of the proteins identified so far, UmuD′, UmuC, and RecA* were shown to facilitate replication across UV-light-induced lesions, yielding both error-free and mutagenic translesion-synthesis products. Similar to UV lesions, N -2-acetylaminofluorene (AAF), a chemical carcinogen that forms covalent adducts at the C8 position of guanine residues, is a strong replication-blocking lesion. Frameshift mutations are induced efficiently by AAF adducts when located within short repetitive sequences in a two-step mechanism; AAF adducts incorporate a cytosine across from the lesion and then form a primer-template misaligned intermediate that, upon elongation, yields frameshift mutations. Recently, we have shown that although elongation from the nonslipped intermediate depends on functional umuDC + gene products, elongation from the slipped intermediate is umuDC + -independent but requires another, as yet biochemically uncharacterized, SOS function. We now show that in DNA Polymerase III-proofreading mutant strains ( dnaQ49 and mutD5 strains), elongation from the slipped intermediate is highly efficient in the absence of SOS induction—in contrast to elongation from the nonslipped intermediate, which still requires UmuDC functions.