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Biomedical subjects

D Schlessinger

Publications and source records attributed to D Schlessinger.

At least 181 records · Page 10Linked to original sources
PubMed1980

pMB9 plasmids bearing the Salmonella typhimurium his operon and gnd gene.

A plasmid containing the entire Salmonella typhimurium his operon was constructed from plasmid pM89 and an EcoRI fragment of phi 80 his imm lambda DNA. The recombinant pST41 also includes the glucose 6-phosphate dehydrogenase (gnd) gene and has one EcoRI endonuclease cleavage site in the integrated fragment. This plasmid served as a source for the construction of two additional plasmids, one carrying the OGDC-region of the his operon and the other a CBHAFIE segment of the his gene along with the gnd gene. The presence of the his operon in the constructed plasmids was confirmed by hybridization to S. typhimurium his RNA. The location of the gnd gene in the CBHAFIE fragment of the his gene was confirmed genetically: after transfection with the plasmid bearing the gnd gene, a gnd recipient gained the capacity to utilize gluconate as a sole carbon source. The DNAs of the three hybrid plasmids were analyzed by gel electrophoresis. By comparing the EcoRI endonuclease cleavage pattern of these three hybrid plasmids with the DNA cleavage pattern of phi 80 his imm lambda, phi 80 imm lambda and lambda phages, the EcoRI cleavage map of phi 80 his imm lambda was obtained.

Bacteriophage lambda↗
PubMed1980

Lactose operon transcription from wild-type and L8-UV5 lac promoters in Escherichia coli treated with chloramphenicol.

In cells treated with chloramphenicol and the inducer isopropyl-beta-D-thiogalacto-pyranoside, messenger ribonucleic acid transcription from the wild-type lac promoter was not detected. Transcription occurred from the mutant UV5-L8 promoter. The transcripts were of variable length; some included the whole Z gene. No major site of transcription arrest within the Z gene was apparent.

Chloramphenicol↗
PubMed1979

Acid ribonuclease from HeLa cell lysosomes.

An acid ribonuclease has been purified from HeLa cell lysosomes. The specific activity of the RNase in lysosomes is 8-fold higher than that in nuclei and 15-fold higher than that in the postlysosomal fraction. The purified enzyme showed no detectable DNase, phosphodiesterase, phosphatase, or alkaline RNase activity. The acid RNase binds to Con A-agarose and is inferred to be a glycoprotein. It has a low isoelectric point at pH 3.0 to 3.5, and the optimal pH for activity is between 5.0 and 5.5. The enzyme requires no divalent cation for optimal activity and is totally inhibited by 1 mM Cu2+ or Hg2+. Monovalent cations including Na+, K+, and NH4+ stimulate the activity in low ionic strength buffer. The enzyme degrades rRNA faster than tRNA, and tRNA faster than poly(U); poly(A) and poly(C) are highly resistant. The products from rRNA are mostly oligonucleotides with 3'-phosphate ends. An acid RNase is also present in the lysosomes of L-cells grown in a medium free of serum; it is probably identical to the one described here.

Animals↗
PubMed1979

SV40-transformed human diploid cells that remain transformed throughout their limited lifespan.

Of ninety-one subcultured foci of SV40-transformed WI-38 human diploid fibroblasts, none yielded cells that grew indefinitely, but all cells in each subculture continued to produce T antigen and to look morphologically transformed throughout their lifespan. These results are consistent with the commitment theory of fibroblast senescence, but predict that a special transformation event is necessary to accout for the rare survivors.

Antigens, Neoplasm↗
PubMed1979

Classification of polyene antibiotics according to chemical structure and biological effects.

Fourteen polyene antibiotics and six of their semisynthetic derivatives were compared for their effects on potassium (K(+)) leakage and lethality or hemolysis of either Saccharomyces cerevisiae or mouse erythrocytes. These polyene antibiotics fell into two groups. Group I antibiotics caused K(+) leakage and cell death or hemolysis at the same concentrations of added polyene. In this group fungistatic and fungicidal levels were indistinguishable. Group I drugs included one triene (trienin); tetraenes (pimaricin and etruscomycin); pentaenes (filipin and chainin); one hexaene (dermostatin); and one polyene antibiotic with unknown chemical structure (lymphosarcin). Group II antibiotics caused considerable K(+) leakage at low concentrations and cell death or hemolysis at high concentrations. The fungistatic levels were clearly separable from fungicidal. This group included the heptaenes (amphotericin B, candicidin, aureofungin A and B, hamycin A and B), and five of their semisynthetic derivatives (amphotericin B methyl ester, N-acetyl-amphotericin B, hamycin A and B methyl esters, and N-acetyl-candicidin). Nystatin, classified as a tetraene, and its derivative, N-acetyl nystatin, also were in this group.

Animals↗
PubMed1978

Separation and characterization of two activities from HeLa cell nuclei that degrade double-stranded RNA.

Two enzymatic activities that degrade double-stranded RNA have been partially purified from HeLa cell nuclei using reoviral [3H]RNA as the substrate. The two active fractions, separated by chromatography on phosphocellulose, are designated PC I and PC II. Both fractions degrade a variety of double-stranded RNAs with an absolute requirement for a divalent cation. However, they are distinct by at least five criteria. 1)PC I degrades a variety of single- and double-stranded RNAs, single- and double-stranded DNAs, and DNA.RNA hybrids, in addition to double-stranded reoviral RNA. In contrast, PC II has maximal activity with reoviral RNA, some activity with rRNA, and much less activity with the other substrates. 2) Analyses of reaction products by sucrose gradient centrifugation and chromatography on Sephadex G-100 and DEAE-cellulose indicate that, PC I cleaves reoviral RNA endonucleolytically to a final mixture of mono- and oligonucleotides, whereas the only acid- or alcohol-soluble products of PC II are 5'-XMPs produced exonucleolytically. 3) PC I activity is stimulated 2-fold more by MnCl2 than by MgCl2, whereas PC II activity is stimulated 3-fold more by MgCl2 than by MnCl2. 4) PC I activity is inhibited by NaCl concentrations as low as 10 mM, whereas PC II requires 50 to 80 mM NaCl for optimal activity. 5)Estimated by their sedimentation rates in glycerol gradients, PC I and PC II have apparent molecular weights of 55,000 and 20,000, respectively.

Cell Nucleus↗
PubMed1978

Coupling of lac mRNA transcription to translation in Escherichia coli cell extracts.

In an extract containing all the components for lac gene expression except washed ribosomes, lac mRNA formation was increased 4- to 6-fold by the addition of washed ribosomes. The formation of beta-galactosidase mRNA and enzyme showed very different dependency on added ribosomes. Enzyme was formed in proportion to the number of ribosomes added, whereas 10% of the standard level of ribosomes promoted full levels of transcription. Consistent with their action in vivo, chloramphenicol and erythromycin blocked the ribosome-dependent lac transcription. The same inhibition was seen with RNA pulse-labeled for 1 or 5 min, so that the effect was truly a blockage of formation rather than an increased hyperlability of nascent mRNA. The effect was specified for some RNA species, as it is in vivo: phage lambda N gene transcription was increased rather than inhibited in the presence of chloramphenicol. Chloramphenicol did not stop lac transcription as a result of its blockage of formation of the regulatory nucleotide tetraphosphate (ppGpp), because addition of the nucleotide did not restore mRNA formation in chloramphenicol-treated extracts. Rather, the data are consistent with the ideas that one or a few ribosomes moving closely behind RNA polymerase can prevent its arrest and that, when ribosome movement is blocked by chloramphenicol, the RNA polymerase is exposed to factors that provoke premature RNA chain termination.

Cell-Free System↗
PubMed1977

Purification and some novel properties of Escherichia coli RNase II.

RNase II of Escherichia coli (EC 3.1.4.23) has been purified to apparent homogeneity. The K+-activated diesterase activity against poly(U), which defines RNase II, cochromatographs with activity against T4 mRNA or pulse-labeled E. coli RNA successively on DEAE-cellulose, hydroxyapatite or phosphocellulose, and Sephadex G-150 columns. Activities with both substrates are selectively reduced to less than 2% of the wild type level in a newly isolated mutant strain, S296, or after thermal inactivation in a mutant strain with temperature-sensitive RNase II. RNase II releases 5'-XMP without a lag as its only detectable alcohol-soluble produce from all substrates and has an apparent molecular weight of 80,000 to 90,000 in both nondissociating and sodium dodecyl sulfate-polyacrylamide gels. The pure enzyme shows the standard K+ activation against poly(A), poly(U), or poly(C), but only a slight preference for K+ over Na+ ions with T4 mRNA or pulse labeled E. coli RNA as substrate. Uniformly labeled E. coli rRNA or tRNA is degraded little if at all.

Enzyme Activation↗
PubMed1977

Mechanism of the inhibition by RNA of the RNA polymerases of Histoplasma capsulatum.

4 S RNA isolated from the dimorphic fungus Histoplasma capsulatum inhibited the DNA-dependent RNA polymerase activity of the yeast phase of this fungus. Inhibition was specific for initiation, and resulted from binding of the RNA to the enzyme. Among a variety of synthetic polynucleotides tested, only poly(G) and oligo(dG) were effective inhibitors, suggesting a role for guanines or guanine-rich sequences of RNA in the inhibition reaction.

DNA-Directed RNA Polymerases↗