traY and traI are required for oriT-dependent enhanced recombination between lac-containing plasmids and lambda plac5

Carter, J R; Porter, Ronald D.

doi:10.1128/jb.173.3.1027-1034.1991

Cited by 26 publications

(23 citation statements)

References 28 publications

(28 reference statements)

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“…The few cases of recA-independent loss of a lac duplication on F9 128 (9 3 10 À4 ) may reflect deletions arising on the plasmid, which has a very high rate of genetic rearrangement stimulated by its conjugative replication origin (Silver et al 1980;Seifert and Porter 1984a,b;Tlsty et al 1984;Carter and Porter 1991;Carter et al 1992).…”

Section: Resultsmentioning

confidence: 99%

Duplication Frequency in a Population of Salmonella enterica Rapidly Approaches Steady State With or Without Recombination

Reams¹,

Kofoid²,

et al. 2010

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Tandem duplications are among the most common mutation events. The high loss rate of duplication suggested that the frequency of duplications in a bacterial population (1/1000) might reflect a steady state dictated by relative rates of formation (k F ) and loss (k L ). This possibility was tested for three genetic loci. Without homologous recombination (RecA), duplication loss rate dropped essentially to zero, but formation rate decreased only slightly and a steady state was still reached rapidly. Under all conditions, steady state was reached faster than predicted by formation and loss rates alone. A major factor in determining steady state proved to be the fitness cost, which can exceed 40% for some genomic regions. Depending on the region tested, duplications reached 40-98% of the steady-state frequency within 30 generations-approximately the growth required for a single cell to produce a saturated overnight culture or form a large colony on solid medium (10 9 cells). Long-term bacterial populations are stably polymorphic for duplications of every region of their genome. These polymorphisms contribute to rapid genetic adaptation by providing frequent preexisting mutations that are beneficial whenever imposed selection favors increases in some gene activity. While the reported results were obtained with the bacterium Salmonella enterica, the genetic implications seem likely to be of broader biological relevance.

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Section: Resultsmentioning

confidence: 99%

Duplication Frequency in a Population of Salmonella enterica Rapidly Approaches Steady State With or Without Recombination

Reams¹,

Kofoid²,

et al. 2010

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“…This hypothesis was inspired by the fact that recombination between homologous alleles residing on the FЈ and on the chromosome is 20-to 50-fold higher than recombination between the same alleles when both are on the chromosome (43). This enhancement requires the presence of oriT in cis to one of the alleles, the expression of the conjugal nicking functions, and the RecA-RecBCD pathway for recombination (7,8). These requirements are the same as those for adaptive mutation in FC40.…”

Section: Adaptive Mutation To Lacmentioning

confidence: 95%

Induction of a DNA Nickase in the Presence of Its Target Site Stimulates Adaptive Mutation in Escherichia coli

et al. 2002

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Adaptive mutation to Lac؉ in Escherichia coli strain FC40 depends on recombination functions and is enhanced by the expression of conjugal functions. To test the hypothesis that the conjugal function that is important for adaptive mutation is the production of a single-strand nick at the conjugal origin, we supplied an exogenous nicking enzyme, the gene II protein (gIIp) of bacteriophage f1, and placed its target sequence near the lac allele. When both gIIp and its target site were present, adaptive mutation was stimulated threeto fourfold. Like normal adaptive mutations, gIIp-induced mutations were recA ؉ and ruvC ؉ dependent and were mainly single-base deletions in runs of iterated bases. In addition, gIIp with its target site could substitute for conjugal functions in adaptive mutation. These results support the hypothesis that nicking at the conjugal origin initiates the recombination that produces adaptive mutations in this strain of E. coli, and they suggest that nicking may be the only conjugal function required for adaptive mutation.When populations of microorganisms are exposed to nonlethal selection, mutations that relieve the selective pressure can appear, a phenomenon called adaptive mutation (4,5,15). The mutational process is not directed to specific targets, because nonselected mutations also occur (14). But the process does require the presence of the selective agent; e.g., simply starving cells for a carbon source does not result in mutations (4, 5).Adaptive mutation has been extensively studied in Escherichia coli strain FC40. This strain cannot utilize lactose (i.e., it is Lac Ϫ ) because of a ϩ1-bp frameshift mutation that affects the lacZ and lacY genes (6, 40). Although the Lac Ϫ allele, ⌽(lacI33-lacZ), is slightly leaky, the amount of ␤-galactosidase produced is not sufficient to allow the cells to grow on medium containing lactose as the only carbon source (4, 13). For ease of genetic manipulation, the lac and proAB operons are carried on an episome, FЈ 128 , and the corresponding region is deleted from the chromosome.During nonselective growth, Lac ϩ revertants of FC40 appear at a rate of about 10 Ϫ9 per cell per generation; when incubated on lactose minimal medium, Lac ϩ revertants arise for about a week at a constant rate of about 10 Ϫ7 per cell per day (4, 14). The Lac ϩ mutations arising during lactose selection are distinguished from the Lac ϩ mutations that arise during nonselected growth in several ways: (i) whereas mutations arising during nonselected growth consist of a variety of deletions and duplications that can revert the ⌽(lacI33-lacZ) allele, adaptive Lac ϩ mutations are almost exclusively Ϫ1-bp frameshifts in runs of iterated bases (20, 50); (ii) unlike mutations occurring during nonselective growth, adaptive mutations require recombination functions, specifically E. coli's RecARecBCD pathway for double-strand break (DSB) repair (4, 32); (iii) to achieve the high level of recombination-dependent mutation in FC40, the Lac Ϫ allele must be on the episome and one or more co...

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“…All the events central to the AM model-duplication, amplification, segregation, and the side effect of SOS mutagenesisare likely to be stimulated by the single-stranded DNA and DNA ends produced by the transfer replication origin of the conjugative plasmid (21,47). The transfer functions (tra) of these plasmids are known to cause intense recombination (8,26,43,52), and conjugative plasmids are prone to amplification (35,46,53). Selection promotes lac reversion very poorly when lac is in the chromosome (15,17,36,48), and selective amplification of chromosomal genes has been shown to be a slow process (34), presumably because of a paucity of DNA ends.…”

Section: Role Of Conjugative Plasmidsmentioning

confidence: 99%

Adaptive Mutation: How Growth under Selection Stimulates Lac ⁺ Reversion by Increasing Target Copy Number

Roth

Andersson

2004

J Bacteriol

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From the time of Darwin until about 1950, a controversy continued over whether selective stress induces mutations or only affects the relative reproductive success of organisms with different genotypes (30). The controversy was resolved by the classic experiments of Luria and Delbrück (27) and of Lederberg and Lederberg (25), who showed that some bacterial mutants arise prior to application of the selection that allows their detection and thus could not have been caused by selective conditions. However, these experiments used lethal selections and therefore did not eliminate the possibility that another fraction of total mutations might be formed in response to stress and be detected only by nonlethal selection. Shapiro and Cairns et al. reopened the controversy by pointing out this caveat and presenting data that seemed to support stress-induced mutation (7,45).Because very few genetic systems behave in ways that suggest stress-induced mutation, the rare cases that seem to exhibit such behavior have attracted close attention. In one case, mutants were later shown to preexist selection (14,28,29,44). For the system devised by Cairns and Foster (5), we suggest that reversion occurs by a multistep process initiated prior to selection and the appearance of stress-induced mutagenesis results from growth under strong selection. THE CAIRNS-FOSTER EXPERIMENT AND WHAT IT SEEMS TO SAYThe Cairns-Foster system employs a leaky lac (ϩ1) frameshift mutation carried on an FЈ plasmid in Escherichia coli (5). During nonselective growth, this mutation reverts at a rate of about 10 Ϫ8 /cell/generation. However, when 10 8 mutant cells are plated on minimal lactose medium, about 100 Lac ϩ revertant colonies accumulate over 6 days (12, 13). The initial models (directed mutation [DM] and hypermutation [HM]; see below) assumed that selection induces Lac ϩ revertants in the nongrowing parent population. This population showed little or no increase in associated mutations compared to the 100-fold increase in lac revertant number (12, 55), suggesting that mutation is directed preferentially to sites that improve growth. In later experiments, a fourfold increase in unselected mutations was seen in the parental Lac Ϫ population and interpreted as evidence for general hypermutability (3). However the effect on the parent population is small compared to the 100-fold stimulation of reversion and therefore supports the idea of directed mutation. REGULATED MUTABILITY-DM OR HM?The DM model suggested that cells sense the nature of the stress and direct mutation to targets that relieve it (7, 13). Two possible mechanisms for DM (9, 50, 51) were ultimately rejected for this system (13). The DM model fell from favor, but was not eliminated (in our opinion), when it was discovered that Lac ϩ revertants (but not the stressed population as a whole) pass through a temporary generally hypermutable state (55). Hall suggested the HM model, by which general mutagenesis might appear to be directed (18). He proposed a control mechanism that senses stress and ...

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traY and traI are required for oriT-dependent enhanced recombination between lac-containing plasmids and lambda plac5

Cited by 26 publications

References 28 publications

Duplication Frequency in a Population of Salmonella enterica Rapidly Approaches Steady State With or Without Recombination

Duplication Frequency in a Population of Salmonella enterica Rapidly Approaches Steady State With or Without Recombination

Induction of a DNA Nickase in the Presence of Its Target Site Stimulates Adaptive Mutation in Escherichia coli

Adaptive Mutation: How Growth under Selection Stimulates Lac ⁺ Reversion by Increasing Target Copy Number

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traY and traI are required for oriT-dependent enhanced recombination between lac-containing plasmids and lambda plac5

Cited by 26 publications

References 28 publications

Duplication Frequency in a Population of Salmonella enterica Rapidly Approaches Steady State With or Without Recombination

Duplication Frequency in a Population of Salmonella enterica Rapidly Approaches Steady State With or Without Recombination

Induction of a DNA Nickase in the Presence of Its Target Site Stimulates Adaptive Mutation in Escherichia coli

Adaptive Mutation: How Growth under Selection Stimulates Lac + Reversion by Increasing Target Copy Number

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Adaptive Mutation: How Growth under Selection Stimulates Lac ⁺ Reversion by Increasing Target Copy Number