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Biomedical subjects

W R Folk

Publications and source records attributed to W R Folk.

At least 73 records · Page 4Linked to original sources
PubMed1978

Overmethylation of DNAs by the EcoRI methylase.

EcoRI methylase is able to catalyze methy incorporation into DNA at sequences other than the canonical EcoRI site. At high enzyme concentrations and over a wide range of pH and ionic strengths, EcoRI methylase modifies polyoma DNA (which contains one EcoRI site) at a number of sites. This modification prevents EcoRI endonuclease activity, and thus is presumably at or near the EcoRI sequences (5') NAATTN.

Adenine↗
PubMed1977

EcoRI cleavage and methylation of DNAs containing modified pyrimidines in the recogintion sequence.

The effects of substituents at position 5 in the pyrimidine ring of a variety of phage DNAs upon EcoRI endonuclease and methylase activities have been examined. The replacement of cytidine in DNA with glucosylated hydroxymethylcytidine confers resistance to cleavage by the EcoRI endonuclease. Substitution of thymidine in DNA by hydroxy-methyluridine(a change in the methyl at position 5 of thymidine for a hydroxymethyl) lowers the maximal velocity of endonucleolytic cleavage 20-fold, but has no detectable effect upon the Km. Substitution of thymidine in DNA by uridine (a change in the methyl at position 5 of thymidine for a hydrogen atom) has no effect upon either the maximal velocity or the Km. The effect of these modifications upon EcoRI methylase activity was markedly different. DNA containing glucosylated hydroxymethylcytidine is methylated as well as normal DNA. DNA containing uridine or hydroxy-methyluridine, in place of thymidine, is much more poorly methylated than normal DNA. These different sensitivities of the EcoRI endonuclease and methylase to modifications in the pyrimidine rings of DNA suggest there are significant differences in the manner by which these enzymes recognize and bind to the canonical EcoRI sequence.

Bacteriophages↗
PubMed1976

Iodination of DNA. Studies of the reaction and iodination of papovavirus DNA.

Iodination of DNA by the reaction originally described by S. L. Commerford ((1971), Biochemistry 10, 1993) is extremely sensitive to the secondary structure of the DNA. Cytidines in denatured simian virus 40 (SV40) DNA react at a slightly slower rate than free cytidine monophosphate; hydrogen-bonded cytidines in SV40 form I DNA are iodinated considerably more slowly; elimination of the negative supercoils in form I DNA by conversion to form II or form III reduces reactivity even further. The residual reactivity of form II or form III duplex DNA is not due to preferential iodination of unpaired cytidines near phosphodiester bond breaks; rather iodination occurs throughout the molecule. Cytidine monophosphate has been used as a model for DNA, to enable spectral measurements of its reaction with iodine and T1C13. At temperatures above 42 degrees C and at pH 5.0, formation of 5-iodocytidine is limited by the rate of formation of an intermediate, probably 5-iodo-6-hydroxydihydrocytidine. At lower temperatures, the conversion of intermediate to product is rate limiting, but can be accelerated by lowering the pH. By appropriate adjustment of pH, or temperature, the formation of intermediate or its conversion to product can be accelerated. Iodination destabilizes the DNA duplex. Iodocytosines in SV40 DNA are preferentially removed by S1 nuclease. Heavily iodinated DNA does not reassociate normally, but DNA with only 5-10% of its cytosines iodinated appears to reassociate with normal kinetics, if duplex formation is measured by hydroxylapatite chromatography. Conditions are described to permit preparation of DNA, which reassociates normally, having a specific activity of 10(8) cpm/mug.

Binding Sites↗
PubMed1976

Polyoma genome in hamster BHK-21-C13 cells: integration into cellular DNA and induction of the viral replication.

When grown at 39.5 degrees C, BHK-21 C-13 cells transformed by A gene mutants of polyoma virus contain viral sequences that are predominantly associated with cellular DNA pelleted in the Hirt lysis procedure. At this temperature, in cells that are inducible for viral DNA replication (Folk, 1973), the majority of the viral genomes are covalently joined with cellular DNA's containing repetitious sequences. Upon a shift to 31 degrees C, free viral genomes appear and are replicated. Coupled with the replication of the free viral genomes at 31 degrees C is an increase in the viral genomes associated with cellular DNA.

Cell Line↗
PubMed1975

The nucleotide sequences of the two glutamine transfer ribonucleic acids from Escherichia coli.

The nucleotide sequences of the two glutamine tRNA species in Escherichia coli K12 have been determined. Sufficient data was obtained to order unambiguously the products of complete RNase digestion of tRNA2Gln, and all but one oligonucleotide from tRNA1Gln. The sequence of tRNA1Gln was established by analogy with tRNA1Gln, as the two tRNAs are very similar, differing by only 7 residues out of 75. tRNA1Gln has the anticodon NUG, where N is a modified nucleotide which is likely to be a derivative of 2-thiouridine, and is specific for the codon CAA. tRNA1Gln has the anticodon CUG, and is specific for the codon CAG (Folk, W. R., and Yaniv, M. (1972) Nature 237, 165). The complete sequences of the tRNAGln species are: See journal for formula (Unique residues are enclosed in parentheses, with the residue in tRNA1Gln above that in tRNA2Gln.).

Anticodon↗
PubMed1973

Induction of virus synthesis in polyoma-transformed BHK-21 cells.

BHK-21 cells were transformed with polyoma virus mutants Ts-a and Ts-25 by using a temperature shift from 31 to 39 C at 5 days after infection so that rescuable transformants could be isolated. Clones which yielded virus after fusion with mouse cells were scored and maintained at 39 C in the presence of antipolyoma virus antiserum. Generally, no infectious viral deoxyribonucleic acid (DNA) could be found in Hirt supernatant fractions of these lines when maintained at 39 C, but DNA-DNA reannealing measurements detected two to six viral genomes per diploid cell genome in the nuclear DNA. Fusion with permissive cells was not necessary to induce the synthesis of infectious virus; cell lines shifted to 31 C produce the equivalent of 100 viral genomes per cell after 5 days. In some cell lines up to 1% of the cells formed infectious centers upon a shift to 31 C, and 100% of the subclones of a line were inducible. Growth at 31 C selected for a noninducible population which was still transformed.

Animals↗