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K G Lark

Publications and source records attributed to K G Lark.

54 records · Page 3Linked to original sources
PubMed1969

Relation of the segregative origin of chromosome replication to the origin of replication after amino acid starvation.

Cultures of Escherichia coli 15T(-) and K-12 were labeled with (3)H-thymine before, during, and after amino acid starvation. The number of labeled segregating units was measured by autoradiography of microcolonies derived from the labeled cells. In both strains, labels inserted before starvation and during starvation appeared to segregate as if incorporated into the same polynucleotide strands. However, labels inserted during and after starvation segregated as if incorporated into different polynucleotide strands. In view of previous data, it was concluded that replication after amino acid starvation originates from the region of the chromosome which serves as the origin for replication during normal growth and division.

Autoradiography↗
PubMed1967

Segregation of deoxyribonucleic acid in bacteria: association of the segregating unit with the cell envelope.

Cells of the gram-positive organism Lactobacillus acidophilus R-26 were labeled with (3)H-thymine to measure the segregation of radioactive deoxyribonucleic acid (DNA) into daugher cells. Such cells were found to contain 8 conserved units of DNA which would correspond to two replicating chromosomes per cell. Fluorescent antibody (FA) against this organism was used to demonstrate that portions of the cell surface (2 to 4 units per cell) were conserved during growth and division. The permanent association of DNA with these conserved cell surface units was measured by combining autoradiography with FA techniques. DNA synthesized immediately before FA labeling was not associated with the fluorescent cell surface, whereas DNA synthesized a generation previously was. The results are consistent with a model in which DNA becomes permanently fixed to the cell surface when it is first used as a template.

Animals↗
PubMed1966

Segregation of sister chromatids in mammalian cells.

Segregation of sister chromatids in embryonic mouse cells in primary tissue culture is not random. In mitosis those chromatids replicated on a DNA template synthesized during the preceding division cycle are separated from those constructed on a template synthesized two division cycles previously. Segregation in cells of the Chinese hamster follows a similar, but less pronounced, pattern.

Animals↗
PubMedDate not supplied

The RecE recombination pathway mediates recombination between partially homologous DNA sequences: structural analysis of recombination products.

Escherichia coli generalized recombination, utilizing the RecA RecB recombination pathway, requires large stretches (70-200 bp) of complete DNA sequence homology. In contrast, we have found that the RecE pathway can promote recombination between DNA with only short stretches of homology. A plasmid containing 10 partially homologous direct repeats was linearized by digestion with specific restriction enzymes. After transformation, a RecE+ (sbcA) host was able to circularize the plasmid by recombination between partially homologous direct repeat sequences. Recombination occurred in regions of as little as 6 bp of perfect homology. Recombination was enhanced in the regions adjacent to restriction sites used to linearize the plasmid, consistent with a role of double-strand breaks in promoting recombination. A mechanism is proposed in which the 5' exonuclease, ExoVIII, produces 3' single-stranded ends from the linearized plasmid. These pair with other sequences of partial homology. Partial homologies in the sequences flanking the actual join serve to stabilize this recombination intermediate. Recombination is completed by a process of "copy and join." This recombination mechanism requires less homology to stabilize intermediates than the degree of homology needed for mechanisms involving strand invasion. Its role in nature may be to increase genomic diversity, for example, by enhancing recombination between bacteriophages and regions of the bacterial chromosome.

Base Sequence↗
PubMedDate not supplied

Teaching a new dog old tricks: identifying quantitative trait loci using lessons from plants.

Locating quantitative trait loci (QTL) in mammalian systems has proven difficult due to the lack of genetic control and reproducibility, as well as the expense of maintaining sufficiently large populations for genotyping and phenotyping. In plants, populations of recombinant inbred lines (progeny bred to homozygosity from a single cross) do not have these problems. Methods developed to identify QTL in a recombinant inbred soybean population provide a basis for analysis of a suitable mammalian population, such as Portuguese water dogs in the United States. The more than 6,000 dogs have accurate pedigrees, available phenotypic data and samples for genotyping, as well as interesting quantitative trait variation. The computer program Georgie allows us to choose large subpopulations with desirable characteristics such as high degrees of consanguinity that capture some of the benefits of recombinant inbred lines in plants. Computer simulations extending methods developed for simpler plant populations indicate that QTL with realistic effects can be identified from such subpopulations. Currently we are developing markers and collecting phenotypic and genotypic data from this population to begin the process of unraveling the genetic basis of quantitative traits in dogs.

Animals↗