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E Grzesiuk

Publications and source records attributed to E Grzesiuk.

9 recordsLinked to original sources
PubMed1992

Mutagenesis of Escherichia coli: a method for determining mutagenic specificity by analysis of tRNA suppressors.

A method for estimating mutagenic specificity in Escherichia coli (argE3, hisG4, thr-1, supE44), based upon the isolation of Arg+ or His+ revertants and identification of tRNA suppressors, is described. The method gives an insight not only into mutagenic pathways but also into the functioning of tRNA. With N-methyl-N'-nitro-N-nitrosoguanidine, 98% of mutations are GC----AT transitions. With N4-hydroxycytidine, 100% are AT----GC transitions. With hydroxylamine, apart from GC----AT transitions, approximately 30% of Arg+ revertants are formed by GC (or AT)----TA transversions. When the chemistry of the mutagenic attack is known, the method allows us to discriminate whether mutations occur on the transcribed or non-transcribed strands of DNA. It has been found that reversion of argE3 to Arg+ is a better monitor of mutagenic pathways than reversion of hisG4 to His+.

Arginine↗
PubMed1987

Recombination of DNAs in Xenopus oocytes based on short homologous overlaps.

Linear molecules of pBR322 and closely related plasmid DNAs were injected into Xenopus oocyte nuclei. Such molecules were degraded unless their ends were recombined. Non-homologous ends were joined rarely, if at all, but measurable recombination was supported by homologous sequences of less than 10 base pairs (bp). The efficiency of recombination increased as the length and degree of homology improved, in the range of about 8-20 bp. The homologous sequences had to be very close to the original molecular ends (within about 20 bp); internal homologies, even when they included better matches, were never used. These observations are best accommodated by a model of recombination which envisions exonucleolytic resection to expose homologous sequences, followed by annealing of single-stranded tails, tidying up and sealing of the new joint. Some of the recombined plasmids had novel tetracycline resistance genes; their properties give some insight into the function of the tet gene product.

Animals↗
PubMed1986

Efficient homologous recombination of linear DNA substrates after injection into Xenopus laevis oocytes.

When DNA molecules are injected into Xenopus oocyte nuclei, they can recombine with each other. With bacteriophage lambda DNAs, it was shown that this recombination is stimulated greatly by introduction of double-strand breaks into the substrates and is dependent on homologous overlaps in the recombination interval. With plasmid DNAs it was shown that little or no recombination occurs between circular molecules but both intra- and intermolecular events take place very efficiently with linear molecules. As with the lambda substrates, homology was required to support recombination; no simple joining of ends was observed. Blockage of DNA ends with nonhomologous sequences interfered with recombination, indicating that ends are used directly to initiate homologous interactions. These observations are combined to evaluate possible models of recombination in the oocytes. Because each oocyte is capable of recombining nanogram quantities of linear DNA, this system offers exceptional opportunities for detailed molecular analysis of the recombination process in a higher organism.

Animals↗
PubMed1981

Replication and expression of fragments of phage PM2 cloned in Escherichia coli K-12.

DNA from PM2 phage was cloned, as HindIII fragments and inserted into the pBR322 vector in E. coli cells. It was shown, that replication of recombined plasmids starts from the pBR322 origin. Transcription of recombinant plasmids in E. coli cells, as well as translation in minicells was demonstrated and attributed to pBR322 and/or PM2 DNA sequences.

Bacteriophages↗