ABSTRACT
This chapter summarizes recent findings about some regulatory features of fimbrial gene systems, and in particular, illustrates those systems that are found in Escherichia coli. Expression of fimbrial genes is commonly affected by the growth conditions of the bacteria, and different stimulatory/inhibitory environmental signals or factors probably influence fimbrial biogenesis of bacteria growing in natural habitats. The output of individual gene products may be quite variable and posttranscriptional mechanisms are presumably important in such operons for the differential gene expression observed. The complex interactions of regulatory proteins in the promoter regions of fimbrial operons may also be part of the mechanism for on-off phase switches. A phase variation mechanism not including any DNA inversion has been revealed by the use of pop::lac hybrid operons and the on-off switching is correlated to specific methylation inhibition at two Dam (deoxyadenosine methylase) sites near the major pap promoter.
