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Introduction to competence and transformation The next part of my research involved studying the way that bacteria are able to take up DNA from their environment. We know that bacteria like Haemophilus influenzae are able to take up new DNA from other bacteria when they are living in a human host. When they do this, they increase the chance that they might acquire new traits that make them more pathogenic or that allow them to escape our immune response. In addition, most bacteria seem capable of competence (a state in which they become able to take up DNA) and be transformed (actually incorporating that DNA into their own genome). So competence and transformation is an important area of research. I developed a model, based on research on H. influenzae and other bacteria, about how the DNA is taken up into the cells in Haemophilus. Model of the DNA uptake mechanism in H. influenzae. A. Following induction of competence, a dedicated transformation pseudopilus is constructed for binding and uptake of exogenous DNA. The pseudopilus is proposed to be a hollow, cylindrical fiber formed by polymerization of PilA and other pseudopilins. Prepilins are exported into the periplasm and the N-terminal signal sequences removed by the action of a prepilin peptidase (PilD). A periplasmic oxidoreductase (Por) is required for proper folding of the pilins. Assembly of the pilins into a pilus structure requires the action of a traffic NTPase (PilB). PilC homologs are required for assembly but their exact role is unknown. Tfp cross the outer membrane through a dedicated secretin (ComE homologs). While the transformation pseudopilus is not expected to extend from the cell surface, ComE is still required for DNA uptake. Disassembly of the transformation pseudopilus also requires the action of a traffic NTPase, possibly PilB or a PilT analogue. B. The DNA is proposed to bind to a dedicated outer membrane protein that recognizes the uptake signal sequence (USS-B). Transport into the periplasmic space likely occurs through the pore formed by ComE and may require disassembly of the pseudopilus. Other organisms require a ComEA homolog that may act to shuttle the incoming DNA to a dedicated transporter for passage across the cytoplasmic membrane (Rec2). One strand of the incoming DNA is degraded by an unknown nuclease (N) prior to, or concomitant with transport into the cytoplasm. An additional protein (T) may be required to provide energy for transportation across the membrane. C. Electron microscopic analysis of competent H. influenzae reveals the presence of membrane blebs (transformasomes) on the cell surface and apparent fusion of the outer and cytoplasmic membranes. This may indicate a need for an additional, unrecognized protein (A) that acts to anchor the membranes together. Model of the H. influenzae DNA uptake mechanism adapted from an N. gonorrhoeae model (Chen and Dubnau, 2004). Abbrieviations: OM: Outer membrane; ML: Murein layer; PS: Periplasmic space; CM: Cytoplasmic membrane.
I wanted to see if I could find any of the missing components of this model. To see how I did this, please continue on.
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