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Biomedical subjects

R H Burdon

Publications and source records attributed to R H Burdon.

At least 55 records · Page 3Linked to original sources
PubMed1982

Hyperthermia and the heat-shock proteins of HeLa cells.

When HeLa cells are subject to hyperthermia, the synthesis of specific heat-shock proteins (HSP) is induced under a variety of thermal conditions. HSP synthesis does not occur at temperatures above 43 degrees C but requires return to a culture temperature of 37 degrees C. Maximal induction appears to be achieved if a brief hyperthermia treatment (10 min, 45 degrees -46 degrees C) is followed by 2 h "development" at 37 degrees C. The induction process requires transcription but not DNA replication, and general cell metabolism is probably also required, as induction does not occur if the heat-treated cells are returned to 4 degrees (rather than 37 degrees C) for development. A small proportion of the HSPs of 72-74 Kd are found in nuclei, but do not appear to bind to DNA. The bulk of these proteins, as well as those at 100 Kd, are cytoplasmic, but none are preferentially associated with mitochondria. Increased synthesis of the 100Kd and 72-74 Kd HSPs was also triggered by pretreatment of the cells with 5 x 10(-5) M sodium arsenite.

Amino Acids↗
PubMed1982

DNA methylation in eukaryotes.

The DNA of higher eukaryotes contains one minor base, namely 5-methylcytosine. The distribution of this minor base between different species and different DNA fractions will be considered together with the actual sequences methylated. The properties of the enzyme responsible for DNA modification will be reviewed, particular note being paid to the efficiency of methylation of different DNA substrates. Various possible functions of the 5-methylcytosine in DNA will be considered and particular attention will be paid to the finding that specific modified bases present in DNA not undergoing transcription are absent in the same genes when these are being actively transcribed.

5-Methylcytosine↗
PubMed1981

DNA methylase during Xenopus laevis development.

The DNA methylase activity present in embryos and cultured cells of Xenopus laevis resembles DNA methylase from mammalian tissues. Little or no activity is found in mature germinal vesicles, though nuclear activity rises rapidly after fertilization. This rise may result in part from a relocation of cytoplasmic enzyme.

Animals↗
PubMed1981

Polypeptides encoded by polyadenylated and non-polyadenylated messenger RNAs from normal and heat shocked HeLa cells.

There is an increased synthesis of proteins in the molecular weight region of 100,000 72,000-74,000 and 37,000 two hours after treatment of HeLa cells for 10 min at 45 degrees C. In vitro translation, using a rabbit reticulocyte cell-free protein synthesising system, of HeLa cell cytoplasmic RNA shows that the prominent 72,000-74,000 Mr heat shock protein band comprises seven polypeptide species (namely alpha d beta gamma delta epsilon zeta) and these polypeptides are directly encoded by both polyadenylated and nonpolyadenylated mRNA.

Animals↗
PubMed1981

Isolation and characterisation of a non-polyadenylated mRNA species with an affinity for poly(adenylic acid) from Friend leukaemia cells.

Utilizing the technique of poly(A)-Sepharose affinity chromatography, it is possible to isolate a novel class of RNA molecules from polysomes of Friend leukaemia cells. These RNA species display messenger RNA-like behaviour. They are released from polysomes on treatment with EDTA and are able to direct polypeptide synthesis in a cell-free protein synthesising system. They appear to be distinct from the polyadenylated mRNAs, as judged by their lack of a 3'-terminal poly(A) tract, by their different size distribution, by their unusual base composition, by the presence of a possible 'uridylate rich' region towards their 3'-end, by their low sequence homology to polyadenylated mRNAs and by the difference in at least some of their translation products.

Animals↗
PubMed1981

The metabolic behaviour of nuclear and cytoplasmic non-polyadenylated RNAs with an affinity for poly(adenylic acid) from Friend murine leukaemia cells.

Using poly(A)-Sepharose and poly(U)-Sepharose affinity chromatography, various classes of nuclear RNA can be distinguished in Friend leukaemia cells. One of these contains a poly(A) tract (poly(A)+-RNA) and another lacks a poly(A) tract but has an affinity for poly(A)-Sepharose (poly(A)-u+-RNA). The stability of these two particular nuclear RNA classes was examined by using a 'pulse-chase' technique involving D-glucosamine treatment. Nuclear poly(A)-u+-RNA was found to decay as a single component with a half-life of about 12 min. In contrast, nuclear poly(A)+-RNA appears to consist of at least two distinct metabolic components with half-lives of about 22 min and 120 min. Furthermore, poly(A)-u+-RNA is transported from the nuclei much more rapidly than the poly(A)+-RNA. The 'pulse-chase' approach also allowed a quantitative estimate to be made of the conversion of nuclear poly(A)+-RNA and poly(A)-u+-RNA to cytoplasmic poly(A)-RNA and poly(A)-u+-RNA.

Animals↗
PubMed1981

Molecular cloning of cDNA sequences coding for the major (beta-, gamma-, delta- and epsilon-) heat-shock polypeptides of HeLa cells.

The method of differential in situ colony hybridisation and the technique of two-dimensional gel electrophoresis of polypeptides synthesized in vitro by mRNAs that hybridise specifically to recombinant plasmids bound to filter discs, have been used to isolate two cDNA HeLa heat-shock clones. Each of these two clones contains the plasmid pBR322 with a cDNA fragment of about 0.3 kb inserted into the PstI site. The two fragments hae different restriction maps. Whilst one of the recombinant plasmids, pHS2, contains a cDNA sequence that hybridises to mRNA coding for the HeLa heat-shock gamma-polypeptide, the other, pHS6, cross-hybridises with mRNAs that code for the HeLa heat-shock beta-, delta- and epsilon-polypeptides.

Base Sequence↗
PubMed1981

The pattern of protein synthesis induced by heat shock of HeLa cells.

While incubation of HeLa cells for 5--10 min at 45 degrees C does not affect subsequent cellular growth and DNA synthesis at 37 degrees C, there is an increased synthesis of specific proteins in the molecular weight region of 100 000, 72 000--74 000 and 37 000. The synthesis of these proteins reaches a maximum 2 h after the heat shock and while the protein themselves are stable, their synthesis declines to normal levels 4 h afterwards. The increased synthesis is blocked by actinomycin D but the addition of cycloheximide or NaF during the "induction' period is without effect.

Cycloheximide↗
PubMed1979

Methylation of mosquito DNA.

Cells of the mosquito Aedes albopictus have 5.6 pg DNA/cell. This DNA is 58 mol% (A + T) and has about 0.03 mol% each of 5-methylcytosine and 6-methylaminopurine. The DNA is largely degraded by the restriction enzyme HpaII showing the virtual absence of the sequence CMeCGG. Small amounts of enzymic activity recovered largely in non-nuclear fractions transfer methyl groups from S-adenosylmethionine to cytosine and adenine.

Aedes↗
PubMed1979

Mouse DNA methylase: methylation of native DNA.

An improved method of purification of DNA methylase from Krebs II ascites cells is reported. The enzyme sediments at 8.3 S on glycerol-gradients and a major band on SDS polyacrylamide gel electrophoresis has a molecular weight of 184 000. Aggregation occurs at low salt and this may interfere with enzymic activity. The preferred double stranded DNA substrate is that rendered partially unmethylated by an in vitro repair mechanism or by isolation from methionine starved cells. Methylation of native partially methylated DNA is favoured under conditions of low salt and high temperature; conditions which encourage 'breathing' of the DNA. Methylation of native, unmethylated DNA also involves breathing but results in formation of a salt resistant tight binding complex between the enzyme and the DNA.

Animals↗
PubMed1978

Genome modification in two lines of baby hamster kidney fibroblasts (BHK-21).

Reasons for the different levels of 5-methyl cytosine encountered in the DNA of two baby hamsters kidney fibroblast lines, BHK-21/C13 and BHK-21/PyY have been investigated. From enzymic studies it does not seem that there are large numbers of potentially methylatable cytosine residues in the C13 line DNA which contains a lower level of 5-methyl cytosine. Rather it is possible that the difference may be due to the reiteration in the PyY strain of certain sequences containing 5-methyl cytosine which simply occur less frequently in the other line.

Cell Line↗