Epigenetic memory of p-pili expression controlled by pap operon in Uropathogen Escherichia coli

摘要

@@The expression of pyelonephritis-associated pili (p-pili) in Uropathogen Escherichia coli (UPEC), which is controlled by pap operon, is a typical model system of phase variation. In spite of its stochastic switching, the operon's state ON or OFF shows a strong epigenetic memory, by which the daughter cell can reproduce the states of their mother with a very high probability. Once the operon is turned off, its OFF to ON transition rate could be as low as 10-4 per cell/generation;The ON to OFF transition rate is also very low, which is 10"2 per cell/generation (Hernday, 2002). The differences in regulatory protein binding affinity can but partially explain this epigenetic memory. According to the existing data, the binding affinities provide only a basis for the establishment of this strong memory, and some other effects are still needed for a fully establishment of the memory.