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Biomedical subjects

K G Lark

Publications and source records attributed to K G Lark.

At least 37 records · Page 2Linked to original sources
PubMed1970

DNA replication in Escherichia coli: location of recently incorporated thymidine within molecules of high molecular weight DNA.

More than 50% of the [(3)H]thymidine incorporated during short pulses into the DNA of Escherichia coli 15T(-) can be extracted by alkali as high molecular weight DNA. Density gradient centrifugation and digestion with exonuclease I suggest that these large pieces of DNA are composed of newly synthesized DNA attached to pre-existing material at the 3' end of the molecule.

Bromouracil↗
PubMed1970

Effect of actinomycin D on the transfer of ribonucleic acid from nucleus to cytoplasm in Lactobacillus acidophilus.

After starvation for deoxyribosides, the deoxyribonucleic acid (DNA) of Lactobacillus acidophilus is restricted to a localized region of the cell. (3)H-uracil is first incorporated into such a restricted region but subsequently is found throughout the cell. This spread occurs despite the absence of protein synthesis and a major reduction in the rate of ribonucleic acid (RNA) synthesis. However, blocking RNA synthesis with actinomycin D restricts incorporation to a localized region of the cell. It is concluded that uracil is first incorporated into RNA in the bacterial nucleus from which it subsequently spreads through the cell. Actinomycin D could prevent this spread by preventing the completion of RNA molecules, which therefore do not dissociate from the DNA template.

Autoradiography↗
PubMed1970

Cytological studies of deoxyribonucleic acid replication in Escherichia coli 15T-: replication at slow growth rates and after a shift-up into rich medium.

We examined the gross nuclear morphology of Escherichia coli 15T(-) grown in different media with doubling times ranging from 22 to 270 min. In slowly growing cells, deoxyribonucleic acid synthesis was measured by autoradiography and shown to occur with greatest probability during the first two-thirds of the division cycle. In such cells, segregation occurred later, at the end of the division cycle rather than at the end of deoxyribonucleic acid replication. Nuclear regions in L-broth cells (22-min doubling time) cannot correspond to separate chromosomes but probably represent regions of replication activity. Segregation of template nucleotide strands was measured after a shift-up from proline M9 or glucose M9 media into L broth. A model is presented to account for the pattern of segregation observed.

Autoradiography↗
PubMed1969

Chromosome replication in Salmonella typhimurium.

The replication of the Salmonella typhimurium chromosome was studied. As with E. coli 15T(-), replication was sequential. After amino acid starvation, replication proceeded from a unique and heritable region of the chromosome. 5-Bromouracil, when substituted for thymine, did not disturb the sequence of replication nor did it initiate extra replication cycles. By labeling the origin and the terminus of the chromosome with (3)H- and (14)C-thymine, respectively, it was possible to determine that the rate of chain elongation decreases as the growth rate decreases. No gap in the replication cycle could be observed.

Amino Acids↗