Interplasmidic illegitimate recombination in Bacillus subtilis

Summary The illegitimate recombination between Staphylococcus aureus plasmids pE194 (or pGG20, the hybrid between pE194 and Escherichia coli plasmid pBR322) and pBD17 (plasmid pUB110 without HpaII C-fragment) was studied in Bacillus subtilis. Cointegrates were generated with the frequency of 1–3x10^-8. Among 22 hybrids analysed 9 types of recombinants were found. Nucleotide sequences of all three parental plasmids were involved in intermolecular recombination. Nucleotide sequencing of recombinant DNA junctions revealed that in 8 cases recombination occurred between short homologous regions (9–15 bp). One recombinant was formed using nonhomologous sites. The similarity was demonstrated between nucleotide sequences of the recombination sites of two types of cointegrates and those used for pE194 integration into the B. subtilis chromosome. Possible mechanisms of illegitimate recombination are discussed.     

Integration of various plasmids into the Bacillus subtilis chromosome

Some features of integration of temperature-sensitive pE194, pGG10 and pGG20 plasmids into the Bacillus subtilis chromosome were studied. Several auxotrophic mutations were obtained using insertion of these plasmids into the chromosome. The sites of plasmids for illegitimate recombination were determined. It was shown that the integration into the Bac. subtilis chromosome is characteristic not only for the plasmid pE194 but is the property of Staphylococcus aureus plasmid pC194 and Escherichia coli pBR322 plasmid. The influence of different Bac. subtilis rec mutations on the frequency of integration was studied.     

A role of Sep1 (= Kem1, Xrn1) as a microtubule-associated protein in Saccharomyces cerevisiae.

Saccharomyces cerevisiae cells lacking the SEP1 (also known as XRN1, KEM1, DST2, RAR5) gene function exhibit a number of phenotypes in cellular processes related to microtubule function. Mutant cells show increased sensitivity to the microtubule-destabilizing drug benomyl, increased chromosome loss, a karyogamy defect, impaired spindle pole body separation, and defective nuclear migration towards the bud neck. Analysis of the arrest morphology and of the survival during arrest strongly suggests a structural defect accounting for the benomyl hypersensitivity, rather than a regulatory defect in a checkpoint. Biochemical analysis of the purified Sep1 protein demonstrates its ability to promote the polymerization of procine brain and authentic S.cerevisiae tubulin into flexible microtubules in vitro. Furthermore, Sep1 co-sediments with these microtubules in sucrose cushion centrifugation. Genetic analysis of double mutant strains containing a mutation in SEP1 and in one of the genes coding for alpha- or beta-tubulin further suggests interaction between Sep1 and microtubules. Taken together these three lines of evidence constitute compelling evidence for a role of Sep1 as an accessory protein in microtubule function in the yeast S.cerevisiae.     

Maternal influence upon the V-type gene position effect in Drosophila melanogaster.

Summary We have studied the influence of various factors on the V-type position effect of the white gene transposed to heterochromatin as a result of different chromosome rearraugements in D. melanogaster. Variegation due to the white gene position effect is much weaker if the flies have received Dp(1;3)w^vco from parental males, and not females. The origin of the chromosome rearrangement does not have this influence in the case of T(1;4)w^m5 or has it to insignificant extent in the case of In(1)w^m4. The Y-chromosome in maternal genome strongly suppresses Dp(1;3)w^vco-induced variegation even in the progeny which has not received an extra Y-chromosome but only if this progeny gets Dp(1;3)w^vco from the same female. The low temperature (16° C) at which parental females have developed, considerably affects the position effect in the progeny with Dp(1;3)w^vco, whereas the temperature of males' development has no influence at all. The maternal temperature effect occurs also when Dp(1;3)w^vco has come down from the father, though it is stronger if the mother subjected to low temperature treatment bore the rearrangement. The influence of temperature seems to take effect at the final stages of oogenesis.The data obtained lead one to suppose that the influence of genotypic and external factors on variegation is passed to the next generation of flies in different ways. The direction of crosses and additional Y-chromosome heterochromatin in the maternal genome seem to affect variegation in the progeny through changes in the properties (structure) of the chromosome rearrangement expressing the position effect. As to the temperature of the mothers development, only a small part of its influence may be accounted for by the same mechanism, whereas most of the temperature influence seems to be passed on through other components of the nucleus or through the cytoplasm.     

Dds20 operates in Cds1-independent mechanism of tolerance to UV-induced DNA damage in <Emphasis Type="Italic">Schizosaccharomyces pombe</Emphasis> cells

Repair of DNA double-stranded breaks caused by ionizing radiation or cellular metabolization, homologous recombination, is an evolutionary conserved process controlled by RAD52 group genes. Genes of recombinational repair also play a leading role in the response to DNA damage caused by UV light. Cells with deletion in gene dds20 of recombinational repair were shown to manifest hypersensitivity to the action of UV light at lowered incubation temperature. Epistatic analysis revealed that dds20 ⁺ is not a member of the NER and UVER gene groups responsible for the repair of DNA damage induced by UV light. The Dds protein has functions in the Cds1-independent mechanism of UV damage tolerance of DNA.     

Analysis of mutations in the mat1 region of Schizosaccharomyces pombe strain with the deletion of gene rhp55 +

DNA double-strand breaks may occur both under the action of various exogenous factors and in the course of cell metabolism processes, in particular, upon mating type switching in yeast. Genes belonging to the epistatic group RAD52 are known to repiar such DNA damage. Molecular defects in mating type switching occurring after the deletion of gene rhp55 ⁺ encoding the paralog of recombinational protein Rhp51, which is a functional homolog of Escherichia coli RecA, were studied in fission yeast. Analysis of stable nonswitching segregants in h ⁹⁰ rhp55 mutants with unchanged configuration of the mating type switching locus but with a drastically decreased level of double-strand DNA break formation at the mat1:1 locus demonstrated changes in DNA sequences within the region responsible for the generation of the breaks. These changes might have resulted from incorrect gene conversion upon repair of double-strand DNA breaks in Schizosaccharomyces pombe rhp55 mutants.     

Phosphorylation of Rad55 on serines 2, 8, and 14 is required for efficient homologous recombination in the recovery of stalled replication forks

DNA damage checkpoints coordinate the cellular response to genotoxic stress and arrest the cell cycle in response to DNA damage and replication fork stalling. Homologous recombination is a ubiquitous pathway for the repair of DNA double-stranded breaks and other checkpoint-inducing lesions. Moreover, homologous recombination is involved in postreplicative tolerance of DNA damage and the recovery of DNA replication after replication fork stalling. Here, we show that the phosphorylation on serines 2, 8, and 14 (S2,8,14) of the Rad55 protein is specifically required for survival as well as for normal growth under genome-wide genotoxic stress. Rad55 is a Rad51 paralog in Saccharomyces cerevisiae and functions in the assembly of the Rad51 filament, a central intermediate in recombinational DNA repair. Phosphorylation-defective rad55-S2,8,14A mutants display a very slow traversal of S phase under DNA-damaging conditions, which is likely due to the slower recovery of stalled replication forks or the slower repair of replication-associated DNA damage. These results suggest that Rad55-S2,8,14 phosphorylation activates recombinational repair, allowing for faster recovery after genotoxic stress.     

Interaction of bacteria of the genus Bartonella with the host: inhibition of apoptosis, induction of proliferation, and formation of tumors

The bacteria of the genus Bartonella are the causative agents for earlier not diagnosed or re-emergent diseases of the humans, danger of which increases in relation with increasing number of persons with the disturbed immune status. Bartonellae are intracellular parasites, the places of their habitation in the humans and animals are the endothelial cells of blood vessels and erythrocytes. The modern data concerning major factors of the Bartonellae virulence and host-bacteria interactions were considered and discussed in this article. The induction of the type IV secretion system, effector protein transmission, inhibition of the endothelial cells apoptosis, and induction of their proliferation lead to formation of new blood vessels and tumors.     

Recombinational Repair in Schizosaccharomyces pombe: A Role in Maintaining Genome Integrity

Recombinational DNA repair was first detected in budding yeast Saccharomyces cerevisiaeand was also studied in fission yeast Schizosaccharomyces pombeover the recent decade. The discovery of Sch. pombehomologs of the S. cerevisiae RAD52genes made it possible not only to identify and to clone their vertebrate counterparts, but also to study in detail the role of DNA recombination in certain cell processes. For instance, recombinational repair was shown to play a greater role in maintaining genome integrity in fission yeast and in vertebrates compared with S. cerevisiae. The present state of the problem of recombinational double-strand break repair in fission yeast is considered in this review with a focus on comparisons between Sch. pombeand higher eukaryotes. The role of double-strand break repair in maintaining genome stability is discussed.