Genetics: Analysis and Principles 5th Edition by Robert Brooker

Exercise 35

An operon in the bacterium Salmonella typhimurium has the following arrangement:

a.
The promoter for this operon is contained within a TE. The H2 gene encodes a protein that is part of the bacterial flagellum. The rH1 gene encodes a repressor protein that represses the H1 gene, which is found at another location in the bacterial chromosome. The H1 gene also encodes a flagellar protein. When the promoter is found in the arrangement shown here, the H2/rH1 operon is turned on. This results in flagella that contain the H2 protein. The H1 protein is not made because the rH1 repressor prevents the transcription of the H1 gene. At a frequency of approximately 1 in 10,000 (which is much higher than the spontaneous mutation rate), this strain of bacterium can "switch" its expression so that H2 is turned off and H1 is turned on. Bacteria that have H1 turned on and H2 turned off can also switch back to having H2 turned on and H1 turned off. This switch also occurs at a frequency of about 1 in 10,000. Based on your understanding of transposons and recombination, explain how switching occurs in Salmonella typhimurium. Hint: Take a look at solved problem S2.Problem S2
Recombination involves the pairing of identical or similar sequences, followed by crossing over and the resolution of the intertwined helices. On rare occasions, the direct repeats or the inverted repeats within a single TE can align and undergo homologous recombination. What are the consequences when the direct repeats recombine What are the consequences when the inverted repeats recombine