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Biomedical subjects

A Toussaint

Publications and source records attributed to A Toussaint.

At least 73 records · Page 4Linked to original sources
PubMed1980

Inversion induced by temperature bacteriophage mu-1 in the chromosome of Escherichia coli K-12.

Induction of the Mu prophage of a lysogenic HfrP4X strongly stimulates the early transfer of the purE gene, which is located far from the origin of transfer. By using a rec- Mu cts62 X lysogenic donor, it was established that this process reflects the inversion of the origin of transfer in part of the Hfr population. Hfr's with inverted polarity of gene transfer were isolated; their analysis suggests that two Mu genomes in opposite orientation surround the inverted DNA fragment. Due to the presence of the Mu genome of the invertible G segment, homologous regions in the same orientation can appear in Mu genomes in opposite orientation. In a Rec+ background, Hfr's with inverted polarity (i) return to their original polarity of transfer by recomination between the two inverted Mu and (ii) produce new F' strains by recombination between the two similarly oriented G segments.

Bacteriophage mu↗
PubMed1979

Mini-muduction: a new mode of gene transfer mediated by mini-mu.

We compared the transducing properties of Mucts62 and Mucts62/mini-Mu lysates, using Mu immune and non immune Recqnd recA recipient strains. The Mu/mini-Mu lysates transduced all bacterial markers tested 10 times more efficiently than the Mucts62 lysates in Rec + recipients. Most of the transductants obtained after infection with the Mu/mini-Mu lysates result from the substitution of the mutated gene of the recipient by the wild type allele from the donor, most probably carried on the gigantic variable end linked to the mini-Mu genome. Moreover the Mu/mini-Mu lysates gave a new type of Rec-independent transduction that we called mini-muduction. Mini-muduction requires the activity of Mu gene A and provides transductants which carry the transduced marker surrounded by two mini-Mu genomes similarly oriented, and inserted at random location in the recipient chromosome. The mini-Mu/transduced DNA/mini-Mu structures are able to transpose spontaneously, for instance into a transmissible plasmid, in the presence of Mu gene A product.

Bacteriophage mu↗
PubMed1978

Phage Mu-1 mediated transposition: a tool to study the organization of ribosomal protein genes in Escherichia coli.

Phage Mu-1 mediated transposition has been used to map genes coding for ribosomal proteins and elongation factor G inside transcriptional units. The data indicate that 1) the str A and fusA genes belong to the same operon, 2) the spcA and strA genes are expressed independently, 3) the spcA gene is located in a different transcriptional unit to that of the eryA and eryB genes.

Coliphages↗
PubMed1978

Chromosomal rearrangements by an IS2 insertion in phage Mu-1.

We have isolated and characterized a mutant of temperate phage Mu-1 carrying an IS2 insertion in the middle of its beta region. This mutant gives rise spontaneously to secondary mutants which have deletions of different sizes adjacent to IS2. One particular derivative however, was found to have acquired an additional insertion sequence adjacent to IS2. This derivative gave rise to tertiary mutants carrying a deletion next to the tandem insertion. The tandem insertion was located at the same place in the Mu beta region as another 2.6 kb insertion independently isolated by Chow et al. (1977) and was found to be homologous to that insertion. The properties of this particular secondary mutant show that Mu phage particles lacking their S end are defective for growth and lysogenisation.

Chromosome Aberrations↗
PubMed1978

Stimulation of deletions in the Escherichia coli chromosome by partially induced Mucts62 prophages.

Deletion of bacterial DNA fragments is stimulated in induced Mucts62 lysogens. The host genes located proximally to the prophage are more frequently lost than those which are unlinked to the Mu genome. Genes located on either side of a Mu genome are deleted in the same manner. Like the other Mu-induced rearrangements, this process is recA independent and requires the participation of Mu DNA, as indicated by the fact that a phage genome always replaces the deleted genes. Data are presented which strongly suggest that both ends of the Mu genome are involved in deletion formation.

Chromosomes, Bacterial↗
PubMed1975

Model for the enchancement of lambde-gal integration into partially induced Mu-1 lysogens.

Temperate phage Mu-1, which is able to integrate at random in its host chromosome, is also able to mediate integration of other circular deoxyribonucleic acid, as a lambda-gal mutant unable to integrate by itself. After mixed infection with lambda-gal and Mucplus, galplus transductants are recovered that have the lambda-gal integrated in any circular permutation, sandwiched between two complete Mu genomes in the same orientation, the whole Mu-lambda-gal-Mu structure being found at any location in the bacterial chromosome. Here we show that such a lambda-gal can integrate in an induced Mu lysogen. In this case the lambda-gal is again in any circular permutation, between two Mu in the same orientation, but it is always located at the site of the original Mu prophage, and the two surrounding Mu have always the same genotype as the original Mu prophage. Active Mu replication functions are not essential for that process to occur. This suggests that bacterial replication may generate two Mu copies that in some way can regenerate a Mu attachment site that recombines with the lambda-gal. A model is presented that accounts for these observations, may be helpful for understanding some complex features of Mu development, and may possibly offer a basis for explaining spontaneous duplications.

Chromosomes, Bacterial↗