Complexity of the ultraviolet mutation frequency response curve in Escherichia coli B/r: SOS induction, one-lesion and two-lesion mutagenesis

Abstract

Three distinct sections of the ultraviolet mutation frequency response (MFR) curve toward tryptophan prototrophy have been demonstrated in Excherichia coli B/r WP2 trp thy and its uvrA derivative in log-phase growth in minimal medium. The initial section, which appears fluence-squared, may reflect the necessity, if mutation is to result, for induction of two lesions, one located within the potentially mutated genetic locus and the other damaging deoxyribonucleic acid replication and resulting in inducation of the error-prone SOS repair function. A second linear section is ascribed to the continued induction, after exposure above that sufficient for complete SOS expression, of isolated lesions which lead to mutation in potentially mutated loci. The third section demonstrates an increased rate of mutagenesis and suggests the induction of two lesions in proximity which result in additional mutations. Split-exposure studies support the inducible nature of the SOS function and suggest that mutation frequency decline (MFD) is due to exicion resulting from or related to the prevention of SOS induction by inhibition of protein synthesis. Preirradiation tryptophan starvation of the uvr+ strain for 30 min decrease MFR in the first and second sections of the curve. Reduction of MFR in the third section requires more prestarvation time and is blocked by nalidixic acid. The decreased MFR of the first and second sections ascribed to promotion of postirradiation MFD based on excision and that of third section to completion of the chromosome during the prestarvation period.

Ultraviolet mutagenesis and inducible DNA repair in Escherichia coli.

“…3 seem to support the "one-lesion + SOS induction" hypothesis at low UV fluences and the "two-lesion" hypothesis at higher UV fluences. Both Witkin (238) and Doudney (63) have recently concluded that some UV-induced mutations in E. coli are caused by single UV photoproducts, whereas others are caused by the interaction of two closely spaced UV lesions, and that neither hypothesis is wholly correct nor wholly incorrect. Witkin (238) has distinguished between single premutational UV lesions that require error-prone SOS repair but are not, in themselves, sufficient signals for the induction of SOS repair activity ("SOS-mutable, SOS-noninducing" lesions), and UV lesions generated by the interaction of two UV photoproducts, which are not only targets for SOS repair activity but are also effective inducers of SOS repair ("SOS-mutable, SOS-inducing" lesions).…”

“…3) would be hard to explain. Variation in the proportions of the two kinds of premutational lesions might be expected in different genes, or even in the same gene under different conditions, and could account for the complexity and variability characteristic of mutation frequency response curves (63). The UV Lesion Responsible for Induction of SOS Functions The composite induction curves for prophage induction and W-reactivation shown in Fig.…”

Modification of UV-induced mutation frequency and cell survival of Escherichia coli B/r WP2 trpE65 by treatment before irradiation

“…The growth medium, culture conditions, UV irradiation technique, and determinations of viability and mutation frequency were as previously described (7). The growth medium was Davis minimal salts (Difco Laboratories)-glucose (10 glliter) supplemented with L-tryptophan (20 ug/nml).…”

“…Although plots of mutation frequency response to UV radiation on exponential coordinates are traditional, Doudney (6)(7)(8), using plots of mutation frequency response with arithmetic coordinates, noted that with Eschrrichia coli B/r WP2 trpE65 (an ochre nonsense mutant strain) a more complex pattern of mutation frequency response is discernible. With intermediate fluences a linear mutation frequency response was seen, but with lower and higher fluences nonlinear responses, increasing with fluence, were evident.…”

Survival and mutagenesis in UV-irradiated phage: Multi-hit kinetics of mutation induction and lack of indirect induction by infection with UV-irradiated phage of error-prone repair

“…In many cases it has been observed that mutation induction in Escherichia coli follows dose-squared kinetics (BRIDGES et al 1973, DOUDNEY 1975, MENNIGMANN 1972, SARGENTINI and SMITH 1979, WITKIN 1976. At very low and very high doses the kinetics are of a different type (DOUDNEY 1976, KAPLAN 1978, SARGENTINI and SMITH 1979). This reflects the necessity for co-operation of two UV-induced lesions and/or their repair to give one mutational event.…”