Natural Competence - Mechanisms of DNA Uptake

Mechanisms of DNA Uptake

In the natural world DNA usually becomes available by death and lysis of other cells, but in the laboratory it is provided by the researcher, often as a genetically engineered fragment or plasmid. During uptake, DNA is transported across the cell membrane(s), and the cell wall if one is present. Once the DNA is inside the cell it may be degraded to nucleotides, which are reused for DNA replication and other metabolic functions. Alternatively it may be recombined into the cell’s genome by its DNA repair enzymes. If this recombination changes the cell’s genotype the cell is said to have been transformed. Artificial competence and transformation are used as research tools in many organisms (see Transformation (genetics)).

In almost all naturally competent bacteria components of extracellular filaments called type 4 pili (a type of fimbria) are involved in the transformation process, and DNA may enter the cells via DNA translocase. Some bacteria cut the DNA into short pieces before transporting it; others can take up very long intact fragments and circular plasmids. The details of the uptake machinery are not yet fully characterized in any system.