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Replication forks temporarily or terminally pause at hundreds of hard-to-replicate regions around the genome. A conserved pair of budding yeast replisome components Tof1-Csm3 (fission yeast Swi1-Swi3 and human TIMELESS-TIPIN) act as a "molecular brake" and promote fork slowdown at proteinaceous replication fork barriers (RFBs), while the accessory helicase Rrm3 assists the replisome in removing protein obstacles. Here we show that the Tof1-Csm3 complex promotes fork pausing independently of Rrm3 helicase by recruiting topoisomerase I (Top1) to the replisome. Topoisomerase II (Top2) partially compensates for the pausing decrease in cells when Top1 is lost from the replisome. The C terminus of Tof1 is specifically required for Top1 recruitment to the replisome and fork pausing but not for DNA replication checkpoint (DRC) activation. We propose that forks pause at proteinaceous RFBs through a "sTOP" mechanism ("slowing down with topoisomerases I-II"), which we show also contributes to protecting cells from topoisomerase-blocking agents., (© 2020 Shyian et al.; Published by Cold Spring Harbor Laboratory Press.)

Invasive and cytopathogenic properties of clinical strains of Helicobacter pylori in the cell culture Hep-2 have been studied. It has been established that H. pylori possesses high invasive and adhesive capacity. It has been shown that H. pylori takes considerable effect on the indices of mitotic activity, such as mitotic index (MI), level of pathogenic mitoses; it also stimulates the appearance of pathologies connected with the disturbance of mitotic apparatus and damage of chromosomes. H. pylori in the cell culture Hep-2 was observed to evoke a tendency to neoplastic growth, loss of contact inhibition, resulting in the cells piling up on each other with formation of the transformation loci.

It has been established that addition of antioxidants: cystamine, ionol, alpha-tocopherol to protective media (saccharose-gelatin agar) does not affect considerably viability of lyophillized cells of cultures Myxococcus xanthus UCM 10041 and Polyangium cellulosum UCM 10043. Experimentally obtained and predicted data on the survival of cells of M. xanthus UCM 10041 and P. cellulosum UCM 10043 are the values of the same order which evidences for the possibility of the use of quick test for prediction of myxobacteria cells survivability under long-term storage.

Viability of myxobacteria strains Myxococcus xanthus UNCM 10041, Polyangium cellulosum UNCM 10043, Archangium gephyra UNCM 10001 stored by the methods of lyophilization, cryoconservation, drying on paper discs, suspending in distilled water or physiological solution under a layer of mineral oil. The best results on viability preservation of all three studied strains were obtained when using the method of cryoconservation. It has been shown that the strains M. xanthus and A. gephyra preserve the best viability during two years of observations when stored in liquid nitrogen and dried on paper discs. Strain P. cellulosum preserves viability for two years when stored in liquid nitrogen and in suspensions on distilled water and physiological solution.

Lipopolysaccharide (LPS) and its structural components: lipid A, O-specific polysaccharide (O-PS) and oligosaccharide core (OG-core) have been isolated from Cytophaga lytica. 3-Oxytetradecanoic (40.8%) and dodecanoic (28.7%) are the predominant fatty acids of lipid A; pentadecanoic (6.8%), 3-oxyhexadecanoic (6.5%) as well as hexadecanoic (5.4%) acids have been found as well. The content of the rest of fatty acids is inconsiderable (2.3 to 0.5%). OG-core contained monosaccharides both typical of the most Gram-negative bacteria (glucose, mannose, galactose, rhamnose, glucosamine) and rarely occurring one-arabinose. O-PS is represented by glucose, mannose, rhamnose, glucosamine, galactosamine as well as unidentified hexosamine.

The experiments on mice and cell culture of a kidney of green monkey Vero have shown that lipopolysaccharides (LPS) of the studied strains 81 and 92 of Cytophaga sp. were nontoxic. They were less active as compared to LPS of other Gram-negative bacteria as to interferon-inducing activity. A comparative study of initial and dephosphorylated LPS has shown that phosphate groups were not responsible for the interferon-inducing activity of LPS of Cytophaga genus representatives.

Nucleotide composition, genome size and DNA homologies were studied for strains Cytophaga johnsonae DSM 425, C. pectinovora DSM 6368, C. saccharophyla DSM 1811, C. aquatilis DSM 2063, C. flevensis DSM 1076, C. lytica ATCC 23 178, C. arvensicola DSM 3695, C. heparina DSM 2356. A considerable difference in GS-bases level between species of genus Cytophaga (33.3-34.9 mol %) and incertae sedis species (C. heparina and C. arvensicola) (45.0-46.7 mol. %) was shown. The differentiation between freshwater and soil, on the one hand, and seawater species, on the other hand, was determined. The degree of DNA-resemblance between them was 2-13%. The existence of relationship between freshwater and soil species was demonstrated. The homology in DNA of freshwater and soil species (C. johnsonae, C. pectinovora and C. saccharophyla) was 22-37%. The heterogeneity of genus Cytophaga and the necessity of its revision are supported.

The biosynthesis of exocellular proteases by Aspergillus candidus is inhibited if a source of energy, carbon and nitrogen is added to the medium lacking one of these elements. The biosynthesis is not entirely inhibited if a sulfur source is added to the medium deficient in sulfur. The dynamics of free amino acid pool was studied under the conditions of deficiency of carbon, nitrogen and sulfur sources. The absence of a carbon or nitrogen source causes a decrease in the overall amino acid pool. The same correlation is true of most individual amino acids, with the exception of valine, tyrosine and phenylalanine (in the absence of a carbon source), or proline and glycine (in the conditions of deficiency of carbon and nitrogen sources). As soon as the limiting source is added to the medium, the amino acid pool rapidly rises. The deficiency of a sulfur source noticeably decreases the level of most amino acids in the cells. The addition of MgSO4 to the medium restores the pool of sulfur-containing amino acids while changes in the concentration of other amino acids remain the same.

The absence of carbon, nitrogen and sulfur sources in the medium was shown to be a prerequisite for the production of exocellular proteases by Aspergillus candidus. The biosynthesis of proteases stops as soon as a limiting substrate is added to the medium. The rate of protease biosynthesis noticeably decreases if proline, alanine, glycine, valine, phenylalanine, serine, threonine, aspartic and glutamic acids are added, particularly during the first hours of incubation. Cysteine increases the delay in the onset of protease biosynthesis. Tryptophan, leucine, asparagine and glutamine considerable decrease the rate of exoprotease biosynthesis throughout the experiment. Arginine, histidine, lysine, ornithine and methionine added to the medium without a carbon source almost entirely inhibit the biosynthesis of exoproteases. A sulfur-deficient fungal mycelium synthesizes exoproteases at a high rate in the medium without a sulfur source whereas sulfate, methionine and cysteine suppress the process. Protein, being the only source of carbon, nitrogen or sulfur in the medium, abruptly decreases the rate of exoprotease biosynthesis.

Aspergillus candidus produced an exocellular protease at a high rate in the absence of nitrogen sources. Nineteen amino acids were added separately as sole nitrogen sources to the medium to study their effect on biosynthesis of exoproteases. All the amino acids were found to repress the biosynthesis, arginine, histidine, lysine and ornithine being most effective among them. Repression of the biosynthesis of exoproteases in the presence of amino acids added as sole nitrogen sources is presumed to be accomplished by ammonium ions which are formed in the course of utilization of amino acids. The level of repression is proportional to the concentration of an amino acid in the medium. Amino acids have no effect on the activity of exocellular proteases synthesized by Aspergillus candidus.