Spontaneous and Ultraviolet-induced Mutation in Escherichia coli: Interaction Between Plasmid and tif-1 Mutator Effects

Abstract

I N T R O D U C T I O NCertain plasmids increase ultraviolet (u.v.) resistance and spontaneous and u .v. mutagenesis in Salmonella typhimurium (Howarth, I 966; MacPhee, 1973 ;Mortelmans & Stocker, 1976). In Escherichia coli, thermally-induced expression of the tif-I mutation similarly causes enhancement of spontaneous and u.v.-induced mutagenesis (Witkin, I 974). The effects of both plasmid expression (MacPhee, 1973 ;Monti-Bragadin, Babudri & Samer, 1976) and tif-I expression (Castellazzi, George & Buttin, 1972) are r e d + dependent. In addition novel DNA synthesis characteristics are found in the presence of plasmids (MacPhee, 1974;Wilkins, 1975) and when t$r is expressed (Radman et al., 1976). These common features prompted us to examine the interaction between the plasmid and tif-1 effects in an attempt to decide whether or not they act through the same mechanism. METHODS Plasmid ~K M I O Iwas transferred from Salmonetla typhimurium TAIOO (McCann et al., 1975) into Escherichia coli W P~ uvvA trp (Hill, 1965) and its non-filamenting t$I sf; derivative WP&NF (Witkin, 1976) using ampicillin selection. Details of the mutation system of m 2 and its derivatives and general methods have been published elsewhere (Bridges et al., 1973). Selective plates for Trp' revertants contained Difco Casamino acids (0.4%, w/v). tryptophan (0.125pg ml-l) and adenine (75 pg ml-l), which has been shown to potentiate tif-1 mutability (Witkin I 974). Bacterial viability was determined by plating appropriate dilutions on the same medium.Exponentially growing cultures were obtained by diluting an overnight broth culture I :IOO into fresh nutrient broth and incubating at 32 "C. and their parental strains at 44 "C for several hours did not result in lethality. However, ~~9 0 1 , unlike the other strains, filamented at this temperature. This was attributed to the presence of the ~K M I O I plasmid, since acridine orange curing of ~~9 0 1 resulted in reversion to the non-filamenting properties of WP44sNF.In Fig. I, spontaneous mutation is plotted as a function of the period of incubation of plates at 44 "C. Strain W'p2 uvrA was unaffected by this treatment (data not shown). Strains W P~~~N Fand cMgo I showed thermal enhancement of spontaneous mutability, although incubation of ~~9 0 1 for longer than 2 h resulted in a reduction in the number of additional mutants. This loss was presumed to relate to the plasmid, since spontaneous mutability of ~~8 9 1 was decreased by incubation at 44 "C ( Fig. I

Mutagenesis and inducible responses to deoxyribonucleic acid damage in Escherichia coli.

“…A sequence with homology to known LexAbinding sequences is located upstream of the mucAB operon (Table 3). The inducibility of the mucAB locus is consistent with the ability of pKM101 to enhance (354,356) and with the synergistic interactions that have been observed between pKM101 and the recA441 mutation (50,79,354). It has been suggested that R46, the parent of pKM101, codes for an element which negatively regulates the expression of the muc genes (81).…”

The muc genes of pKM101 are induced by DNA damage

“…Observations such as the enhancement of Weigle reactivation by pKM101 (24) and the synergistic effects of plasmid pKM101 and recA441 (tif-1) mutations (6,8,32) have indicated that at least some of the effects of pKM101 on mutagenesis and recovery from DNA damage are inducible. In the work described in this paper, we have shown that this inducibility is due, at least in part, to the induction of the mucA and mucB gene products.…”

“…The fact that plasmids pKM101 and R46 are unable to enhance mutagenesis or increase resistance to UV killing in a recA or lexA(Ind-) background (32) suggested that the muc genes of pKM101 might be part of the recA+ lexA+ regulatory network. Furthermore, certain observations, such as the enhancement of Weigle reactivation by pKM101 (33) and the synergistic effects of pKM101 and recA441 (tif-1) mutations (6,8,32), had indicated that some of the pKM101-mediated effects were inducible. However, these physiological experiments did not distinguish between the possibility that a plasmid-encoded gene was induced and the possibility that the plasmid-mediated process required INDUCTION OF muc GENES 1307 the induction of a chromosomally encoded gene but not the induction of a plasmid-encoded gene.…”

Suppression of induction of SOS functions in an Escherichia coli tif-1 mutant by plasmid R100.1

“…This type of plasmid-host interaction has not been observed previously. Other plids have been shown to enhance the expression of SOS mutagenesis and repair functions in recA+ (24,27,39), as well as in tif-strains (8,39). In all cases, the molecular mechanism underlying the interaction has remained obscure.…”