Prophage Mu induction as a tool to analyze mobile genetic element responses to external agents

Abstract

SynopsisMobile genetic elements have been found in the genomes of both procaryotic and eucaryotic organisms. Their unique capacity to move (or transpose) to new chromosomal locations has been critical to their persistence and their ability to affect gene structure and expression. It is conceivable that many physical and chemical agents may induce non-specific DNA transpositions which can result in genomic rearrangements and mutations. We have derived a simple procedure to detect the induction of DNA transposition using bacteriophage Mu, a temperate coliphage whose 37 kilobase linear double-stranded DNA genome behaves as a transposable element during lytic growth and lysogeny. Our assay measures the ability of a chemical to enhance or inhibit the induction of Mu DNA transposition and lytic growth. We have examined a wide variety of mutagens, carcinogens and common chemical compounds and found that most of these agents had little effect on prophage Mu induction and lytic growth at all doses tested. However, many DNAdamaging agents showed a dose-dependent decrease in both the number of plaqueforming units and the number of colony-forming units. We did find that the frequency of prophage Mu induction can be stimulated by certain amino acid analogues, notably azetidine 2-carboxylic acid, but not by others. These results indicate that the response of mobile genetic elements to external agents is not a simple one, and may reflect the necessary presence of an element and cellular regulatory pathway to control these endogenous mutators.

Microsomal‐activated cigarette smoke condensate reduces bacteriophage mu transposase gene expression in rec A+Escherichia coli

“…The effects of external agents on the frequency of transposition of a cell's complement of mobile genetic elements has not been extensively examined (Datta et al, 1983). We have been using the viral transposable element Mu as a model system to study the effect of genotoxic agents on the induction of Mu DNA transposition and transposase gene expression (Shinder et al, 1984;DuBow and Shinder, 1986; Kupelian and DuBow, 1986).…”

“…We have been interested in determining the nature of genotoxic agents that may act by causing the induction of transposition of a cell's complement of mobile genetic elements. We have constructed assay systems to monitor the consequences of external stimuli on DNA transposition (Shinder et al, 1984;DuBow and Shinder, 1986;Kupelian and DUBOW, 1986) using temperate, transposable bacteriophage Mu, whose 37 kilobase pair (kb) double-standard DNA genome behaves like a giant transposon, as a model system. The basic premise of our experiments is that any agent that induces Mu to transpose or express its transposase operon required to provide the enzymes for movement, may have similar effects on other prokaryotic mobile elements.…”

Agents that enhance or reduce movement of mobile genetic elements: Detection in microbial assays and implications for toxicological assessment

“…While conventional mutagens are generally assumed not to increase the frequencies of transpositional events as such (Cairns, 1981;DuBow and Shinder, 1986), it is not at all clear whether this is likely to be true of other types of transposon-associated events such as deletion formation. Indeed, if deletions associated with transposable elements can be enhanced (or diminished) in frequency by environmental agents (including, but not exclusively, conventional mutagens), it may be that such events are more important in the etiology of radiation-induced or chemically induced cancers than is currently believed.…”

“…Further studies with thepolA7 strain of S. typhimurium showed that while the normal amino acid L-methionine caused a significant increase in precise excision of TnlO, its analogue L-ethionine had the opposite effect, causing an almost equally significant reduction (Hafner and MacPhee, 1991). These results, together with those of DuBow and Shinder (1986) showing that the amino acid analogue azetidine-2-carboxylic acid can cause increased transposition of bacteriophage Mu, provide strong evidence that movement of transposons is indeed subject to complex regulatory controls that are very poorly understood at this point in time.…”