Question

Suppose a Salmonella cell acquires a mutation that causes Hin recombinase to become overactive and increase the number of recombination reactions How would repeating a DNA inversion several times in each cell every generation affect this cell's progeny? The daughter cells will not exhibit flagellin and, due to their lack of flagella, bee unable to swim. Daughter cells will express only FliC and will be susceptible to attack by FliC antibodies. The progeny will possess flagella containing both FljB and FliC flagellins and thus will be more susceptible to host immune system attack. Progeny will exhibit flagella containing both FljB and Flic proteins and will move faster than usual FliC flagellin will predominate and the cell will be more susceptible to host immune system attack

Answer 1

Hin recombinase is a 21kD protein composed of 198 amino acid residues. It i a DNA invertase belonging to serine recombinase family of genes. It inverts a 900bp sequence in the Salmonella genome that has a promoter for downstream genes fljA and fljB (flagellar genes). Invertion of the genes leads to alteration in expression and higher flagellar synthesis. This helps the organism to evade host immune response in a faster way.

In the above situation, if Hin recombinase becomes overreactive, then high expression of flagella will take place. Progeny will exhibit flagella with faster moving ability.