Transposition effect of adenine (Dam) methylation on activity of O end mutants of IS50

Tomcsányi, T; Berg, Douglas E.

doi:10.1016/0022-2836(89)90271-4

Cited by 19 publications

(13 citation statements)

References 8 publications

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“…Because Tn5 and IS50 have a higher transposition frequency in Dam-cells than in Dam' cells (11,17,33,36), the selection for sucrose resistance was repeated in Dam-strain DB4351. Sucr mutants were about 200-fold more frequent in derivatives of strain DB4351 carrying plasmids I and II than in the isogenic Dam' strains (Table 1).…”

Section: Resultsmentioning

confidence: 99%

Intramolecular transposition by a synthetic IS50 (Tn5) derivative

et al. 1990

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We report the formation of deletions and inversions by intramolecular transposition of Tn5-derived mobile elements. The synthetic transposons used contained the ISSO 0 and I end segments and the transposase gene, a contraselectable gene encoding sucrose sensitivity (sacB), antibiotic resistance genes, and a plasmid replication origin. Both deletions and inversions were associated with loss of a 300-bp segment that is designated the vector because it is outside of the transposon. Deletions were severalfold more frequent than inversions, perhaps reflecting constraints on DNA twisting or abortive transposition. Restriction and DNA sequence analyses showed that both types of rearrangements extended from one transposon end to many different sites in target DNA. In the case of inversions, transposition generated 9-bp direct repeats of target sequences.Transposable elements are a diverse group of specialized DNA segments that move to new sites in a genome without need for extensive sequence homology. They cause insertion mutations and rearrangements, alter the expression of nearby genes, are found in both procaryotes and eucaryotes, and are valuable as tools for molecular genetics (7).TnS is one of the most intensively studied and widely used of the bacterial transposons. It is a composite element, consisting of terminal inverted repeats of the insertion sequence IS50 and genes for resistance to several antibiotics (6). Transposition is mediated by the cis-acting transposase protein (encoded in IS50), along with host factors. Segments of about 19 bp at each end of IS50 and of Tn5 are essential for transposition (15,27). Tn5 can insert into dozens of sites in any typical gene, a few of which may be used preferentially (hot spots) (8,18). This pattern of relatively low target specificity contributes to the value of TnS as a research tool (2, 3). Early studies showed that the movement of Tn5 and IS50 between DNA molecules generates simple insertions (4, 5), not the cointegrates that are the hallmark of replicative transposition (28), and led to a model in which transposition occurs by a conservative cut-and-paste mechanism (4-6, 22). Several other elements are now also known to undergo conservative transposition (9,16,21), and the present experiments lend support to the nonreplicative transposition model for TnS.Most previous studies of Tn5 transposition have involved movement between different molecules (intermolecular transposition), but insertion into sites within the same molecule (intramolecular transposition) should also occur. Deletion and inversion products are expected in the case of transposition to a site within the element itself: the resultant circular molecules should consist solely of transposon sequences (Fig. 1). A linear fragment, designated the vector because it is outside the transposon, should also be formed and then lost (4-6). Rearranged DNA molecules that were probably products of intramolecular conservative TnS (IS50) transposition were obtained from complex X-IS50-pBR322-* Corresponding author. t...

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Section: Resultsmentioning

confidence: 99%

Intramolecular transposition by a synthetic IS50 (Tn5) derivative

et al. 1990

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“…GATC sites are present within the inside end (IE) of IS50, similar to the case for IS10, and within the Ϫ10 region of the transposase regulatory region (73,253,292). In both IS50 and Tn5, Dam methylation represses tnp promoter activity and transposase binding to the IS50 IE (73,253,292).…”

Section: Regulation Of Cellular Events By the Hemimethylated Dna Statementioning

confidence: 89%

“…In transposition of Tn10, hemimethylated DNA plays two roles: enhancing binding of RNA polymerase to the transposase promoter and enhancing binding of transposase to its DNA target sites (144,181,219). DNA methylation appears to play similar roles in regulating Tn5 transposition (73,161,175,217,253,292). None of these phenomena are heritable since the hemimethylated state of DNA is not heritable, occurring transiently in newly replicated DNA.…”

Section: Introductionmentioning

confidence: 99%

Epigenetic Gene Regulation in the Bacterial World

Casadesús

Low

2006

Microbiol Mol Biol Rev

568

562

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SUMMARY Like many eukaryotes, bacteria make widespread use of postreplicative DNA methylation for the epigenetic control of DNA-protein interactions. Unlike eukaryotes, however, bacteria use DNA adenine methylation (rather than DNA cytosine methylation) as an epigenetic signal. DNA adenine methylation plays roles in the virulence of diverse pathogens of humans and livestock animals, including pathogenic Escherichia coli, Salmonella, Vibrio, Yersinia, Haemophilus, and Brucella. In Alphaproteobacteria, methylation of adenine at GANTC sites by the CcrM methylase regulates the cell cycle and couples gene transcription to DNA replication. In Gammaproteobacteria, adenine methylation at GATC sites by the Dam methylase provides signals for DNA replication, chromosome segregation, mismatch repair, packaging of bacteriophage genomes, transposase activity, and regulation of gene expression. Transcriptional repression by Dam methylation appears to be more common than transcriptional activation. Certain promoters are active only during the hemimethylation interval that follows DNA replication; repression is restored when the newly synthesized DNA strand is methylated. In the E. coli genome, however, methylation of specific GATC sites can be blocked by cognate DNA binding proteins. Blockage of GATC methylation beyond cell division permits transmission of DNA methylation patterns to daughter cells and can give rise to distinct epigenetic states, each propagated by a positive feedback loop. Switching between alternative DNA methylation patterns can split clonal bacterial populations into epigenetic lineages in a manner reminiscent of eukaryotic cell differentiation. Inheritance of self-propagating DNA methylation patterns governs phase variation in the E. coli pap operon, the agn43 gene, and other loci encoding virulence-related cell surface functions.

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“…Work carried out with E. coli Dam indicates that it acts as an efficient de novo methylase, methylating both nonmethylated and hemimethylated GATC sites with similar efficiency (82). Dam plays an important role in regulating the timing and targeting (51) of a number of cellular functions including DNA replication (9,34,41,72), segregation of chromosomal DNA (52,58), mismatch repair (29,48,71), and transposition (19,66,68,77,89). In all of these events, hemimethylated GATC sites, present immediately following DNA replication, control the binding of pro-teins to specific DNA target sites.…”

Section: Dam Familymentioning

confidence: 99%