The isolation of RNA from mammalian cells

Alteration of the permeability of the human erythrocyte membrane to cations by liposome-incorporated amphotericin B

Some effects of liposome-incorporated amphotericin B on the permeability of the human erythrocyte membrane to potassium and sodium ions is reported. The influence of cholesterol and amphotericin B in causing a shift towards smaller and larger liposomes, respectively, is also described. Phosphatidylcholine liposomes containing amphotericin B in a molar ratio of 7.4 +/- 0.1 (mean +/- SD) antibiotic to 1000 phospholipid reduced the initial rates of K+ and Na+ transport across the erythrocyte membrane to 40 +/- 2.6% and 0%, respectively, of their rates in the presence of comparable concentrations of free amphotericin B. Amphotericin B incorporated into liposomes (8.2 +/- 0.15 mumol antibiotic per 1000 mumol total lipid) composed of cholesterol and phosphatidylcholine (in a molar ratio of 3:7) reduced the initial rate of K+ transport to 19 +/- 0.8% of its value measured in the presence of a comparable concentration of free antibiotic. These results suggest that liposomes containing specified amounts of amphotericin B, especially liposomes also containing cholesterol in addition to phosphatidylcholine, could be used as a method of controlling K+ transport across the erythrocyte and possibly other types of cellular membranes, thereby limiting antibiotic toxicity to some mammalian tissues.

Application for PCR technology to subtractive cDNA cloning: identification of genes expressed specifically in murine plasmacytoma cells

We describe a simple method for preparing a renewable source of subtractive cDNA which can be used as a hybridization probe or as insert which can be cloned into a variety of convenient vectors. This has been done by ligating a double-stranded oligonucleotide to each end of double-stranded subtractive cDNA, and then using this oligonucleotide sequence to amplify the heterogeneous population of cDNA molecules using the polymerase chain reaction and thermostable Taq DNA polymerase. This method improves the chances for identifying cDNA clones representing low abundance mRNAs that are expressed differentially. Using this approach, we have identified cDNA clones which detect three different low abundance mRNAs that are expressed in mouse plasmacytoma cell lines but not in mouse pre-B or B lymphoma cell lines.

Characterization of a unique protein produced by influenza A virus recovered from a long-term persistent infection

Virus isolated from a persistent infection initiated in BHK cells with influenza A/WSN/33 (H1N1) produced an unusual pattern of protein synthesis in productive infections of BHK cells: The levels of NP and M1 proteins were slightly reduced compared to an infection with wild-type WSN, while the other proteins (Pb1, Pb2, Pa, HA, NS1, and NS2) were synthesized at very low or undetectable levels. In addition, a new viral protein with an approximate molecular weight of 11 kDa (Pi protein) is made (Frielle et al., Virology 138, 103-117, 1984). When viral RNA was analyzed by the Northern blot technique, a deletion was found in the NS gene segment and in NS1 mRNA; all other RNAs were full-sized. Immunoprecipitation of in vitro translation products demonstrated that the Pi protein reacts specifically with anti-NS1 serum. In addition, the Pi protein, like the NS1 of the parental wild-type virus, accumulated in the nucleus of infected cells. These results indicate that the Pi protein is a mutated form of the NS1 protein encoded by a deleted NS segment and suggest that this mutation may be involved in the expression of the persistent virus phenotype.

Vaccinia rescue of VSV from interferon-induced resistance: reversal of translation block and inhibition of protein kinase activity

Coinfection with vaccinia virus rescues vesicular stomatitis virus (VSV) from the inhibitory effects of interferon (IFN) in mouse L cells. While vaccinia infection does not significantly affect VSV RNA synthesis, coinfection with vaccinia dramatically increases VSV protein synthesis in IFN-treated cells. Evidence is provided that vaccinia inhibits the activity of the IFN-induced dsRNA-dependent protein kinase.

Comparison of in vitro chromatin transcription using E. coli RNA polymerase and wheat germ RNA polymerase B

Use of Escherichia coli RNA polymerase for in vitro transcription of chromatin results in the formation of double-stranded RNA molecules, which consist of a strand of endogenous mRNA and a complementary strand of de novo synthesized RNA. Unless the duplex structures are dissociated prior to isolation of the in vitro transcripts on sulfhydryl agarose columns, the endogenous mRNA can result in over-estimates of in vitro gene-specific transcription. Substitution of wheat germ RNA polymerase B for the bacterial enzyme overcomes this artifact. When mouse fetal liver chromatin is used as template, most of the mRNA synthesized by the plant enzyme is in a single-stranded form. More importantly, this synthesis is directed by a DNA template. Hybridization studies suggest that in vitro transcription of chromatin with wheat germ RNA polymerase B maintains some fidelity to genetic restrictions which operate in vivo.

Hormonal control of mRNA synthesis studied by nucleic acid hybridization

The regulation of protein synthesis by steroids is thought to be due to hormonal effects primarily on mRNA concentration. Experimental evidence to support this conclusion has come largely from the use of DNA probes complementary (cDNA) to mRNA molecules or by translation of the mRNA in vitro. In this review the experimental procedures involved and the application to hormone action of cDNA hybridization will be reviewed. (1) mRNA concentrations can be assayed in tissue RNA samples by hybridization with radiolabelled complementary DNA probes (cDNA). From the rate of hybridization of an mRNA preparation to a cDNA probe it is possible to estimate specific mRNA concentrations and thereby study their hormonal regulation within tissues of subcellular fractions (2) Rates of synthesis of a specific RNA can be measured by hybridization of pulse-labelled RNA with excess cold cDNA as illustrated in studies of the glucocorticoid induction of MMTV RNA. (3) Hormore-induced alterations of mRNA populations as a whole can be investigated. From the kinetics of hybridization of mRNA with its complementary DNA it is possible to estimate the number of different RNA sequences in tissues and to approximate the number of copies of each sequence per cell. Consequently, by comparing mRNA samples isolated from tissues of different hormonal status it is possible to demonstrate specific hormone-inducible mRNA species and, in some cases, identify their translation products.

Quantitation and characterisation of poly(A)-containing messenger RNAs from mouse neuroblastoma cells

Comparison of several isolation procedures for neuroblastoma poly(A)-containing mRNAs shows that the highest percentage recovery of undegraded and biologically active messenger RNAs is obtained using proteinase K prior to phenol extraction. The messenger RNAs thus isolated comprise approximately 1.5% of the total ribosomal RNAs and have negligible contamination with 18 and 28 S RNAs. On denaturing polyacrylamide gels they have an average molecular weight of 6.5-10(5) with a range from 2.2-10(5) to 1.53-10(6). The messenger RNAs have an average poly(A) content of 154 nucleotides. They are highly active in wheat germ in vitro protein synthesizing systems, giving as much as 4.3 pmol [35S]methionine incorporation into total protein per mol of mRNA. This is almost as active as a control globin mRNA preparation.

Properties and synthesis of ribosomal RNA in the free-living nematode Panagrellus silusiae

The normal S values of ribosomes and ribosomal subunits extracted from the free-living nematode. Panagrellus silusiae are similar to those of other eukaryotic organisms. Upon heating (70 degrees C, 15 min) a 5.5-S RNA is released from the larger ribosomal RNA (27 S; 1.40-10(6) daltons). Unlike other protostomes, however, the 27-S rRNA does not dissociate in an orderly manner to yield 18-S components. The electrophoretic mobility of the small ribosomal RNA species (18 S; 0.72-10(6) daltons) is unaltered by heat treatment. The base composition of both Panagrellus rRNA species has a 51% G+C content. Labelling worms with either [Me-3H] methionine or [14C] uridine at various stages of postembryonic development and subsequent analysis of the extracted RNA revealed eight radioactive fractions, two of which were the mature ribosomal RNAs. From both the time sequence of appearance of the eight RNA species and the relative degree of methylation of the various RNA fractions two maturation pathways for ribosomal RNA processing were deduced. A 37-S (3.6-10(6) daltons) RNA is the precursor to both 27-S and 18-S RNA. During processing about two-fifths of the original transcriptional unit is lost. In this organism the "transcribed spacer" regions may be methylated although alternate interpretations have not been precluded.