DNA is constantly exposed to chemical and environmental mutagens, causing lesions that can stall replication. In order to deal with DNA damage and other stresses, Escherichia coli utilizes the SOS response, which regulates the expression of at least 57 genes, including umuDC. The gene products of umuDC, UmuC and the cleaved form of UmuD, UmuD', form the specialized E. coli Y-family DNA polymera...

We compared mutagenic spectra induced by polychromatic near-ultraviolet radiation (near-UV; 300-400 nm) with superoxide anion (O2-) -dependent mutagenesis using a set of Escherichia coli tester strains. Near-UV radiation produced increased frequencies of G:C to A:T transitions, G:C to T:A and A:T to T:A transversions, and small increases in frameshift mutations in wild-type cells. Tester strain...

Previous studies have demonstrated that the Escherichia coli MutHLS mismatch-repair system can process UV-irradiated DNA in vivo and that the human MSH2.MSH6 mismatch-repair protein binds more strongly in vitro to photoproduct/base mismatches than to "matched" photoproducts in DNA. We tested the hypothesis that mismatch repair directed against incorrect bases opposite photoproducts might reduce...

Induced mutagenesis is widely used for selection of microorganisms producing biologically active substances and further improving of their activities. However, it is rarely used toward lactic acid bacteria (LAB) due to their genetic specificity. Determination of LABs sensitivity to UV light and evaluate the effectiveness of UV-induced mutagenesis by positive selection of antibiotic resistant mu...

Many fundamental biological processes have been elucidated by the isolation and analysis of mutants that are defective in such processes. Therefore, the methods to generate mutants are of great importance in model organisms. This unit describes two protocols for mutagenesis of yeast-using ethyl methanesulfate (EMS) and ultraviolet (UV) light. Each of these methods has been used successfully for...

Most mutagenic DNA lesions are noninstructive in the sense that template instruction is either missing or inaccessible during DNA replication, leading to replication arrest. According to the SOS hypothesis, arrested replication induces the expression of SOS factors that force replication past stalled sites at the cost of mutagenesis. We have recently shown that prior UV irradiation of delta rec...

INTRODUCTION............................................................ 61 PROCESSING OF DAMAGED DNA ............................................................ 61 SOS REGULATORY NETWORK ............................................................. 61 Present Model for SOS Regulation ............................................................ 62 SOS Responses ...................................