FIGURE 18.05 Transfection

During viral transfection, an experimenter first isolates pure viral DNA from virus particles. In the diagram, DNA is isolated from P1 virus. Next, the bacterial cell wall is made competent to take up naked DNA (usually by treating with calcium ions or by electroshock). The isolated DNA and the competent bacteria are mixed. If the bacteria take up the P1 DNA, the bacteria will start producing viral particles and burst to release the viral progeny. Thus, viral DNA alone can give the same end result as infection with whole virus particles.

FIGURE 18.06 Competence Pheromones

Dense cultures of S. pneumoniae start producing competence pheromones that induce nearby cells to take up DNA. First, certain cells of the culture produce polypeptide precursors that are digested into a small peptide, or competence pheromone. The small peptide is secreted from the producer cell and binds to a receptor on a nearby cell. The receptor then signals that cell to make proteins used in DNA uptake.

cell, even though in most cases no extra DNA enters the cell. [Note that alterations in the DNA are indeed involved in creating cancer cells, but as a result of mutation.] Supposedly to avoid ambiguity, researchers who use animal cells often use the term "trans-fection" to refer to the uptake of DNA (by transformation!) whether it is of viral origin or not.

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