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J A Heinemann

Publications and source records attributed to J A Heinemann.

11 recordsLinked to original sources
PubMed1997

Yeast plasmids.

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Chromosomes, Artificial, Yeast↗
PubMed1996

Doing the conjugative two-step: evidence of recipient autonomy in retrotransfer.

Bidirectional exchange of genetic information, called retrotransfer, during bouts of bacterial conjugation has drawn the interest of those concerned with the risk of releasing genetically engineered microbes, the fluidity of genes among species, and the mechanism of DNA transport between cells. The phenomenon has generated two models in explanation, both of which yield highly testable predictions. The first model, called the one-step, predicts that the flow of genes from recipient bacteria to donor bacteria is mechanistically distinct from, but dependent on, conjugation between donors and recipients. The second model, called the two-step, predicts that the same genetic requirements and mechanistic constraints apply to the process of gene flow from recipients to donors as for gene flow from donors to recipients. The requirement for expression of at least 10 plasmid-encoded genes in recipients, sensitivity of the reverse flow (recipient to donor) to restriction of DNA transferring from the donor, and the requirement of an additional 30-90 min for DNA to flow from recipients back to donors are predictions of the two-step model and directly refute the one-step model. Retrotransfer of genes to donors during conjugation remains genetically and physically indistinguishable from two successive rounds of conjugation between neighbors.

Conjugation, Genetic↗
PubMed1994

Isolation of a conditional suppressor of leucine auxotrophy in Saccharomyces cerevisiae.

Phenotypically and genotypically (leu2-3, 112) Leu- cells of Saccharomyces cerevisiae gave rise to small colonies on medium devoid of leucine. This only occurred on plates with a high density of Leu- cells or on medium supplemented with limiting quantities of leucine. Cells from these small colonies retained a growth advantage over their parent on limiting leucine supplements even after growth in a non-selecting (rich) medium. Therefore, the growth variants had acquired a heritable change. The phenotype was recessive and due to a change in a nuclear gene unlinked to the LEU2 locus. The phenotype provided a growth advantage only during leucine starvation; growth of the variants was indistinguishable from their parent on medium lacking the other essential supplements (histidine and uracil) required for the growth of the strain. [14C]Leucine uptake assays demonstrated that the variants were better able than their parents to accumulate leucine from their environments, and this ability extended to other hydrophobic amino acids. These results suggest that in the variants an amino acid uptake system has been derepressed rather than there having been reversion or extragenic suppression of the mutation in leucine biosynthesis. We designate the mutant gene responsible for the phenotype lup1 (for leucine uptake). The transport characteristics of the lup1 mutants suggested that LUP1 is a regulatory component of an ammonium-regulated hydrophobic amino acid uptake system.

Amino Acids↗
PubMed1993

Retrotransfer of IncP plasmid R751 from Escherichia coli maxicells: evidence for the genetic sufficiency of self-transferable plasmids for bacterial conjugation.

Gene transfer between organisms is a prime contributor to evolution. Bacterial conjugation is probably the most important mechanism by which genes are spread among prokaryotes and perhaps also contributes to eukaryotic evolution. Conjugation is mediated by plasmids. The mechanism of conjugation remains ill-understood despite progress in the identification, mapping and sequencing of genes required for plasmid transmission. All conjugation-specific genes (those required only for DNA transfer and establishment) identified to date map to plasmids. We found that IncP plasmids could enter and subsequently convert maxicells, which are trapped in a metabolic state that prevents de novo expression of chromosomal genes, into conjugative donors. This suggests that IncP plasmids encode not only necessary functions but indeed all functions specific to DNA transmission. Thus, like viruses, plasmids can convert non-viable cells into gene vectors.

Chromosomes, Bacterial↗
PubMed1993

Retrotransfer in Escherichia coli conjugation: bidirectional exchange or de novo mating?

DNA can be transferred among eubacteria and to plants and fungi by related, plasmid-mediated processes collectively referred to as bacterial conjugation. Conjugation occurs between cells in contact with one another and results in the unidirectional delivery of DNA from a bacterial donor to a recipient. Recent experiments that have reexamined the directionality of DNA flow during conjugation have come to different conclusions, some suggesting that genetic material also flows from recipient cells into the donor and that this process, termed retrotransfer, is likewise directed by donor-encoded functions. Given that bacteria are perhaps united with all living creatures by conjugation, the possibility of gene flow into donor bacteria during conjugation raises interesting evolutionary and biocontainment issues. Here we report that plasmid transmission from bacterial recipients to donors is not a donor-mediated event. Movement of genetic material from recipients to donors was inhibited by streptomycin, which does not inhibit the conjugative donor, indicating that retrotransfer requires gene expression in recipients. Furthermore, retrotransfer was reduced in matings mediated by plasmids that encode strong entry exclusion, to a similar degree as matings between two donors. Therefore we suggest that retrotransfer is in fact newly initiated conjugation between transconjugants and donors.

Bacterial Proteins↗
PubMed1992

The interplay of microbes and their hosts.

Microbes and their hosts exert considerable evolutionary pressure on one another. This brief report of a recent meeting describes the strategies and tactics, and highlights some of the key molecules involved in the complex host-parasite relationship.

Animals↗
PubMed1991

Genetics of gene transfer between species.

Bacteria transfer genetic information to members of at least three of the five biological kingdoms. Gene transfer between species may play the same role as sex between members of a single species, providing genetic diversity and material for repair of genomic damage.

Animals↗