Biomedical subjects

U Nir

Publications and source records attributed to U Nir.

30 records · Page 2Linked to original sources

PubMed1991

In vivo effects of porphyrins on bacterial DNA.

The DNA damage in intact Staphylococcus aureus and E. coli cells induced by photosensitized deuteroporphyrin or hemin is described. Treatment of S. aureus cultures with hemin or photosensitized deuteroporphyrin (Dp) caused time-dependent changes in the plasmidial DNA profiles. The major observation was the disappearance of the plasmid supercoiled fraction. The chromosomal DNA was also affected by hemin and by photosensitized Dp, since its degradation products were detected after exposing the bacterial cells to the porphyrin drugs. Photosensitization of E. coli cells, pretreated with Dp and polymyxin B nonapeptide (PMBNP), also resulted in plasmidial damage. No such damage occurred when E. coli cultures were treated with hemin and PMBNP. The above results can be tightly correlated with the antimicrobial action of porphyrins. Their damage to the bacterial DNA seems to reflect one of the in vivo effects of these porphyrins.

DNA Damage↗

PubMed1990

A murine fer testis-specific transcript (ferT) encodes a truncated Fer protein.

A cDNA for a potential tyrosine kinase-encoding mRNA was isolated from a mouse testis cDNA library. In a survey of eight mouse tissues, a transcript of 2.4 kilobases restricted to testis tissue was found. The mRNA encodes a 453-amino-acid protein of 51,383 daltons, the smallest tyrosine kinase protein ever described. RNA synthesized from the cDNA template directs the synthesis of a 51,000-Mr protein in a cell-free translation system. The carboxy-terminal 409 amino acids are 98 and 90% identical to the carboxy halves of the rat and human Fer proteins, respectively. This suggests that the cDNA represents an alternatively spliced testis-specific fer mRNA and is therefore termed by us ferT. On the basis of the appearance time of the fer mRNA in the testis of maturing neonatal mice, we speculate on the role played by this protein in the development of this organ.

Amino Acid Sequence↗

PubMed1990

The testis-specific transcript (ferT) of the tyrosine kinase FER is expressed during spermatogenesis in a stage-specific manner.

ferT is a testis-specific transcript of FER encoding a truncated version of the potential tyrosine kinase. Using in situ hybridization analysis, we found that ferT was transiently expressed during spermatogenesis and that expression was restricted to spermatocytes at the pachytene stage of meiotic prophase. This pattern of expression is unprecedented by other tyrosine kinases and suggests a role for ferT in a particular stage of spermatogenesis.

Animals↗

PubMed1988

Capturing nuclear sequence-specific DNA-binding proteins by using simian virus 40-derived minichromosomes.

We have used recombinant simian virus 40 (SV40) minichromosomes to retrieve sequence-specific DNA-binding proteins derived from the cell nucleus of COS-7 cells. We showed that the transcription factors AP-1 and Sp1 are stably bound to the SV40 DNA late in viral infection. Under similar conditions, minichromosomes carrying the rat insulin (rINS1) enhancer, which is under negative regulation in COS-7 cells, bound two proteins which mapped to distinct regions of the rINS1 enhancer. The SV40 P element competed for one of these proteins which bound to the region from -198 to -230. This factor may be related to AP-1. The other factor selectively bound a regulatory element in the region from -92 to -124 of the insulin enhancer. These proteins may play a role in regulating the rINS1 enhancer function.

Animals↗

PubMed1986

Regulation of rat insulin 1 gene expression: evidence for negative regulation in nonpancreatic cells.

Two cis-acting elements, the enhancer and the promoter, independently contribute to the cell-specific expression of the rat insulin 1 gene. The activities of these elements are presumably mediated by trans-acting factors. We have performed intracellular competition experiments that suggest the presence of a negative factor(s) that represses the enhancer activity in cells that do not express the insulin gene. In these experiments fibroblast cells (COS-7) were transfected with two plasmids: a test plasmid containing the gene for chloramphenicol acetyltransferase under the control of the thymidine kinase promoter and the insulin enhancer; and a competitor plasmid containing insulin enhancer sequences and the simian virus 40 origin of replication to permit its replication in the recipient cells. The presence of the competitor plasmid led to a 5- to 6-fold increase in chloramphenicol acetyltransferase activity as compared with the activity detected when insulin enhancer was absent from either the competitor or the test plasmid. A 5-fold increase in chloramphenicol acetyltransferase activity was also seen when the rat amylase enhancer was present on the competitor plasmid; in contrast the simian virus 40 enhancer exerted no effect. Efficient derepression required additional sequences downstream from those essential for enhancer activity. We propose that the activity of the rat insulin 1 enhancer is modulated by a negative trans-acting factor(s) that is active in cells not expressing insulin but is overridden by the dominant positive trans-acting factor(s) present in insulin-producing cells.

Animals↗

PubMed1985

Priming affects the transcription rate of human interferon-beta 1 gene.

Priming human fibroblasts with low levels (100 units/ml) of homologous interferon (IFN) prior to induction of gene expression with poly(rI.rC) results in the accumulation of 5-10-fold higher levels of IFN-beta 1 mRNA when compared to induced but nonprimed cells. By run-on transcription assay we have determined that this increase results mainly from increased transcription rate of the IFN-beta 1 gene. We have also shown that priming leads to elevated cytoplasmic steady state levels of two additional RNA species which initiate at the major IFN-beta 1 mRNA initiation site and extend beyond the polyadenylation site for the IFN-beta 1 0.9-kilobase mRNA. Located next to the 3' end of the IFN-beta 1 gene we have also identified a novel poly(rI.rC)-induced gene which like the IFN-beta 1 gene is highly activated in cells primed with IFN prior to poly(rI.rC) induction. However, the expression of another poly(rI.rC)-induced gene located on a different chromosome is only slightly affected by the priming procedure used here. We postulate that IFN priming acts specifically on certain genes rather than by a general potentiation of poly(rI.rC) induction.

Cell Line↗

PubMed1985

Family of human alpha-interferon-like sequences.

An interferon-alpha-like sequence was isolated from a human genomic library by hybridization with a 15-base oligonucleotide. The sequence also showed homology to alpha-interferon and was most closely related to the leukocyte interferon-M gene fragment. The original isolate cross-hybridized to a family of sequences, 10 of which were isolated as clones. Some of these sequences were located within a few kilobases of alpha-interferon genes, consistent with our assignment of several members of the family to human chromosome 9 which also has the beta 1- and alpha-interferon genes.

Amino Acid Sequence↗

PubMed1984

A human IFN-beta 1 gene deleted of promoter sequences upstream from the TATA box is controlled post-transcriptionally by dsRNA.

Induction of IFN-beta 1 RNA was studied in the mouse cell line SR117-21E transformed by a BPV episome containing the human IFN-beta 1 gene deleted of promoter sequences upstream from position -40. Nuclei isolated from these cells synthesize constitutively IFN-beta 1 RNA from the partially deleted promoter. The IFN-beta 1 RNA synthesized by nuclei of uninduced SR117-21E cells is similar to that made by nuclei of poly(rI):(rC)-induced cells, but does not accumulate and hence no IFN is produced unless the cells have been treated either by ds RNA or by cycloheximide. We conclude that the IFN-beta 1 gene has, in addition to the transcription control due to upstream promoter sequences, an additional post-transcriptional control acting on mRNA accumulation and linked to sequences close to the TATA box and RNA start site. Both controls are relieved by ds RNA.

Animals↗

PubMed1982

Interferon-dependent induction of mRNA for the major histocompatibility antigens in human fibroblasts and lymphoblastoid cells.

In human cells treated with interferons, there is an increase in the amount of HLA-A,B,C and beta 2-microglobulin exposed on the cell surface. We have used a cloned HLA-A,B,C cDNA probe to demonstrate by molecular hybridization that this effect of interferon is preceded by a large increase in the amount of HLA mRNA in the cell. This effect was found in five different human cell lines, with purified leukocyte and fibroblast interferons. The increase in HLA mRNA is comparable in its kinetics and dose-response to the induction of (2'-5') oligo(A) synthetase mRNA by interferons. Therefore, interferons seem to activate at least two cellular genes which have different biochemical functions.

Cells, Cultured↗

PubMed1981

Synthesis of human interferon beta 1 in Escherichia coli infected by a lambda phage recombinant containing a human genomic fragment.

DNA from a human adult was fragmented by partial digestion with restriction endonuclease EcoRI and cloned in lambda Charon 4A. Clone C15, with a human DNA insert of 17 X 10(3) bases, was identified as containing a gene for the fibroblast interferon, interferon beta 1. Restriction mapping shows that this gene, located on a 1840-base EcoRI fragment, is not interrupted by introns. Moreover, we show that this human genomic DNA fragment is able to direct the synthesis of active human interferon beta 1 in Escherichia coli. Interferon activity of up to 7 X 10(6) U/l was recovered from phage lysates by chromatography on Cibacron blue--Sepharose, and had the same immunological properties and species specificity as interferon produced by human fibroblasts.

Adult↗

PubMed1980

Interaction between membrane properties and protein synthesis in reticulocytes: influence of trypsinization on [3H]-valinomycin action.

Using [3H]-Valinomycin we show here that two types of sites can be described for this cyclic depsipeptide. A first type is sensitive to low concentration of trypsin while the other, more internal, is uncovered by the use of the protease. Of these two kinds of sites, the more external one seems more concerned with the effect that Valinomycin has on protein synthesis in rabbit reticulocytes. However, when a high concentration of Valinomycin is used, all the sites can be occupied even those which can be revealed only by tripsinization. In this case, even prolonged trypsin action does not result in release of the protein synthesis inhibitory action of Valinomycin. It is concluded that hydrophobic sites are occupied by Valinomycin only after the cell surface has been saturated by hydrophylic bonds with the antibiotic.

Animals↗

PubMed1980

Two interferon mRNAs in human fibroblasts: in vitro translation and Escherichia coli cloning studies.

Two mRNA species that produce biologically active interferon were isolated from human fibroblasts and studied by size fractionation and cloning in Escherichia coli plasmid pBR322. The major fibroblast interferon (Hu IFN-beta 1) is coded for by the smaller of the two mRNAs, an 11S species, 900 nucleotides long, which in cell-free systems yields a 20,000 Mr protein. The second interferon mRNA species (Hu IFN-beta 2) is 14S, about 1300 nucleotides long, and codes for another protein of 23,000-26,000 Mr. The two interferon mRNAs do not cross-hybridize. Both are induced by poly(rI.rC), but IFN-beta 2 mRNA is induced to about 10% in cells by cycloheximide treatment alone whereas under these conditions IFN-beta 1 is not induced.

Biological Assay↗