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Biomedical subjects

J H Taylor

Publications and source records attributed to J H Taylor.

At least 73 records · Page 4Linked to original sources
PubMed1976

Evidence for a four micron replication unit in CHO cells.

CHO cells in culture were synchronized by mitotic selection, allowed to reattach to plastic flasks, and reach S phase in the presence of fluorode-oxyuridine at concentrations known to completely block the synthesis of thymidylate. The cells were released from the block with 3H-thymidine for pulses of 4, 8, 12, 24 and 40 min and DNA fiber autoradiographs prepared. An analysis of the spacing between origins of replication indicates that sites are available at intervals of about 4 mum along most of the DNA. Chain growth proceeds at about 1,000 nucleotides per minute and some of the closely situated sites become continuous, labeled segments after 8-12 min. However, unlabeled segments are still present between the replicated segments after 40 min. The data may be interpreted as evidence for regularly spaced initiation sites which are available in CHO cells, even though only one in 10-15 of these may be utilized for initiation each cycle under normal growth conditions in these cultures.

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PubMed1975

Replication of DNA in mammalian chromosomes. III. Size and RNA content of Okazaki fragments.

A study of sedimentation and buoyant density of Okazaki fragments from mammalian chromosomes along with electron microscopic studies indicate that fragments from about 200 to 1200 nucleotides long may have RNA segments covalently attached. The fragments in some CsCl isopycnic gradients banded in two rather distinct bands. One band corresponds to the density of single-stranded DNA, but the other has a higher buoyant density which could be conferred by a segment of RNA up to 180 nucleotides or more in length. The RNA was not removed by denaturing conditions which separated DNA strands consisting of several thousand nucleotide pairs. When the material of higher buoyant density was spread for electron microscopy under conditions which would extend single-stranded DNA chains, but leave RNA in a coil or bush the chains with a higher buoyant density usually had a bush attached at one end. Under conditions that were thought to favor gap filling over chain elongation near growing forks, the DNA produced by pulse labeling with bromodeoxyuridine had a buoyant density which would indicate substitution to about 15 percent in one chain. If this substitution represents filling of gaps occupied by RNA before the pulse, the segments would be about 180 nucleotides in length assuming about 1,000 nucleotides between each segment.

Animals↗
PubMed1973

Replication of DNA in mammalian chromosomes: isolation of replicating segments.

From Chinese hamster cells, blocked at the beginning of the S phase by treatment with fluorodeoxyuridine and pulse-labeled with [(3)H]thymidine, one can release segments of native DNA containing template polyuncleotide chains and the most recently replicated DNA. The segments, which can be released without shear by lysis at temperatures below the melting point for the double helix, can be separated from both the nascent single chains (Okazaki pieces) and the long strands of native DNA in sodium perchlorate gradients. These 26S segments are equivalent to about 6 mum of native DNA, but may be replication forks rather than linear pieces.

Animals↗