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Biomedical subjects

R H Burdon

Publications and source records attributed to R H Burdon.

At least 73 records · Page 4Linked to original sources
PubMed1977

Poly(A)-binding RNAs from nuclei and polysomes of BHK-21 cells.

The presence in nuclei and cytoplasm of cultured BHK-21/C13 cells (baby hamster fibroblasts) of RNA species with high affinity for poly(A) was detected using either a Millipore-poly(A)-binding assay or columns of poly(A)-Sepharose 4B. The nuclear species which labels rapidly is metabolically unstable and appears to be a specific subclass of heterogenous nuclear RNA. Digestion with T1 RNAase gives rise to a low level (1%) of oligonucleotide fragments of a disperse size range which are relatively rich in uridylate residues. The cytoplasmic species with affinity for poly(A) is similar in size to polyadenylated messenger RNAs and also associates with polysomes. However it appears to be distinct from the polyadenylated messenger RNAs by virtue of an unusual base composition and relative metabolic instability.

Binding Sites↗
PubMed1977

The sequence specificity of vertebrate DNA methylation.

The relative quantity of 5-methyl cytosine in vertebrate nuclear DNA shows species and tissue variation. To determine whether this is due to the action of species or cell specific DNA methylases the sequence specificity of the 5-methyl cytosine distribution in the DNA of a range of cells has been partially characterised. The pattern of methylation was found to be remarkably constant and indicates stringent evolutionary conservation of the characteristics of vertebrate DNA methylation.

Animals↗
PubMed1977

The sequence specificity of a mammalian DNA methylase.

The sequence specificity of an extensively purified DNA methylase preparation from Krebs II mouse ascites cells has been examined. The enzyme appears to be highly sequence dependent. Moreover the sequence distribution of cytosine residues that are methylated, bears a very close resemblance to the sequence distribution of 5'-methyl cytosine found in vivo in a wide range of vertebrate cells and is consistent with methylation of cytosines in the sequence R-Yn-C-R.

Animals↗
PubMed1977

Methylation of nucleosomal and nuclease sensitive DNA.

The proportion of cytosines methylated in the DNA of nucleosome oligomers and of core particles appears indistinguishable from that of total nuclear DNA from CHO cells. However the DNA in nucleoprotein which is initially released from nuclei by treatment with very low levels of micrococcal nuclease and the first 10% of material rendered acid soluble by treatment of nuclei with DNase I are enriched 2 fold in their content of 5 methylcytosine. (Cessation of hydrolysis by nuclease occurs concomitantly with precipitation of nucleosomal core particles).

Cell Line↗
PubMed1975

Comparison of nucleotide sequences in HeLa cell mRNA and hnRNA.

Nearest neighbour analysis of nucleotides in vertebrate DNA has revealed a marked deficiency in the frequency of occurrence of the sequence CpGp. By use of the fingerprinting technique of Sanger et al. (1965) to characterise the nucleotide sequences of HeLa cell hnRNA after T1 RNAase digestion, we have shown that this deficiency also occurs in hnRNA and that it appears to be a general transcript of DNA. This is also true of the hnRNA that contains poly(A). Whilst a deficiency of CpGp occurs also in poly(A) containing mRNA from HeLa cells the deficiency is less marked than in the case of total hnRNA, or poly(A) containing hnRNA. Another difference between mRNA and hnRNA lies in the level of occurrence of the sequence UpApGp. These results are discussed with reference to the possible relationship of hnRNA to mRNA.

Base Sequence↗