R-factor from the natural strain of Salmonella derby carrying a DNA-polymerase gene

A R-factor which determines multiple stability to antibiotics (Cm, Pn, Sm) was found in a Salmonella derby strain isolated from the clinical material. The plasmid was eliminated by treatment with ethidium bromide; the DNA-polymerase activity in the antibiotic-sensitive derivatives measured under conditions optimal for DNA-polymerase I from E. coli was found to be decreased 10-50-fold. Plasmid DNA of S. derby K89 was fractionated by electrophoresis in agarose gel; individual zones I-IV were obtained, using a preparative technique. Upon transformation of S. derby K82 pol- cells, only plasmid DNA in zone II (designed as pSD Cm pol) gave Cm-resistant transformants, in which the DNA-polymerase activity decreased to the normal level. The experimental results pont to the binding of the DNA-polymerase gene to the S. derby plasmid.     

A new role for PGRP-S (Tag7) in immune defense: lymphocyte migration is induced by a chemoattractant complex of Tag7 with Mts1

PGRP-S (Tag7) is an innate immunity protein involved in the antimicrobial defense systems, both in insects and in mammals. We have previously shown that Tag7 specifically interacts with several proteins, including Hsp70 and the calcium binding protein S100A4 (Mts1), providing a number of novel cellular functions. Here we show that Tag7–Mts1 complex causes chemotactic migration of lymphocytes, with NK cells being a preferred target. Cells of either innate immunity (neutrophils and monocytes) or acquired immunity (CD4⁺ and CD8⁺ lymphocytes) can produce this complex, which confirms the close connection between components of the 2 branches of immune response.     

Various characteristics of proteins from HeLa cella specifically binding to the human ALU sequence

Two proteins with molecular weights of 40 and 80 kDa which are able to bind human Alu-repeat in a sequence-specific manner were found in HeLa nuclear extracts. The proteins were partially purified by column chromatography on DEAE-cellulose, phosphocellulose and FPLC MonoQ sorbent. One of the Alu-binding proteins (ABP2 with m. w. of 80 kDa) was found to bind the sequence within the Alu-repeat that has a homology with the T-antigen binding site of SV40, suggesting that ABP2 is the cellular analog of SV40 T-antigen.     

Genetic transformation of somatic cells. XI. The autonomic replication of the cloned DNA of the bovine papilloma virus in NIH/3T3 mouse fibroblasts and the changes in the growth characteristics of the transformed cells

Mouse fibroblasts NIH 3T3 were transfected with the plasmid pBPV (142-6) containing full genome of bovine papilloma virus 1, and focuses of morphological transformation were selected 2-3 weeks later. DNA molecules, containing BPV-1 sequences, were isolated from extrachromosomal fraction of transformed clones suggesting stable autonomous replication of BPV in 3T3 NIH cells. In some rescued plasmids deletions spanning E6, 7 genes of BPV were found. It is suggested that these genes are not essential for morphological transformation and autonomous replication in 3T3 NIH cells. BPV-transformed clones are able to grow in the medium containing low concentration (0.5%) of serum.     

Comprehensive Experimental Investigation of “Jet” and “Bell” Operating Modes in Hall Thruster

Plasma Physics Reports - Two stable operating mode, which were called “jet” and “bell” mode, were observed for Hall thrusters. These modes are distinguished from each other...     

Evidences against vesicle-dependent trafficking and involvement of extracellular proteasomes into cell-to-cell communications

The ubiquitin proteasome system is involved in the regulation of most basic intracellular processes, and deregulation of this system can results in certain kinds of human diseases. Proteolytic core this system, the 20S proteasome, has been found in physiological fluids of both healthy humans and patients suffering from a variety of inflammatory, autoimmune, and neoplastic diseases. The concentration of these extracellular proteasomes has been found to correlate with the diseased state, being of a prognostic significance. The transport mechanisms and functions of these proteasomes, however, are largely unclear. Previous studies revealed that the transport of extracellular proteasomes may occur via microvesicles and exosomes, which led to the hypothesis that extracellular proteasomes are implicated in cell-to-cell communication process. Here we show that microvesicles and exosomes, two major known types of intercellular vehicles, contain no detectable proteasomes. Moreover, neither affinity purified nor naturally released into conditioned medium by donor cells 20S proteasomes could penetrate recipient HeLa cells. Taken together, these results suggest that extracellular proteasomes are unlikely to be involved in the cell-to-cell communication and that their release by cells serve other biological purposes.     

A negative regulator of telomere-length protein trf1 is associated with interstitial (TTAGGG)n blocks in immortal Chinese hamster ovary cells

Telomeres of mammalian chromosomes are composed of long tandem repeats (TTAGGG)n which bind in a sequence-specific manner two proteins-TRF1 and TRF2. In human somatic cells both proteins are mostly associated with telomeres and TRF1 overexpression resulting in telomere shortening. However, chromosomes of some mammalian species, e.g., Chinese hamster, have large interstitial blocks of (TTAGGG)n sequence (IBTs) and the blocks are involved in radiation-induced chromosome instability. In normal somatic cells of these species chromosomes are stable, indicating that the IBTs are protected from unequal homologous recombination. In this study we expressed V5-epitope or green fluorescent protein (GFP)-tagged human TRF1 in different lines of mammalian cells and analyzed distribution of the fusion proteins in interphase nucleus. As expected, transient transfection of human (A549) or African green monkey cells with GFP-N-TRF1 or TRF1-C-V5 plasmids resulted in the appearance in interphase nuclei of multiple faint nuclear dots containing GFP or V5 epitope which we believe to represent telomeres. Transfection of immortalized Chinese hamster ovary (CHO) cell line K1 which have extremely short telomeres with GFP-N-TRF1 plasmid leads to the appearance in interphase nuclei of large GFP bodies corresponding in number to the number of IBTs in these cells. Simultaneous visualization of GFP and IBTs in interphase nuclei of transfected CHO-K1 cells showed colocalization of both signals indicating that expressed TRF1 actually associates with IBTs. These results suggest that TRF1 may serve as general sensor of (TTAGGG)n repeats controlling not only telomeres but also interstitial (TTAGGG)n sequences.     

Focal sites of DNA repair synthesis in human chromosomes

Nucleotide excision repair (NER) is the principle pathway by which the human cells eliminate UV-induced lesions from their genomic DNA. The process can be visualized through the labelling of the nucleotides that are incoporated into repair patches, following the excision of the damaged stretch of DNA. In this study we have visualized sites of DNA repair synthesis (DRS) in human interphase and metaphase chromosomes after very short times (2.5-30 min) of postirradiation labelling in vivo with 5-iododeoxyuridine. A limited number (<50 per nucleus) of discrete nuclear DRS sites were seen in cells fixed immediately after labelling and the sites are also detectable in interphase and metaphase chromosomes visualized 48h after irradiation (3 J/m2). These observations strongly support the view that within a given short time window distinct chromosome domains are under extensive repair while in many other domains NER is slow. They argue against the general distributative NER process but are consistent with a processive scanning of damaged domains.