t Cytosine can spontaneously deaminate to Uracil in DNA. dCTP, a substrate for synthesis of DNA, can also spontaneously deaminate to dUTP. E. coli has an enzyme called Dut (dUTPase) whose job it is to get rid of any dUTP in the cell. Mutations that cause loss of Dut are LETHAL in a strain that is also missing RecA. (In other words, a dut- mutant is alive, a recA- mutant is alive, but a dut- recA- mutant is dead.) An additional mutation in the gene encoding Ung, the Uracil N-glycosylase that removes Uracil from the DNA, restores viability to the dut- recA- double mutant. (The dut- recA- ung- triple mutant is alive.)
What is the mechanism of lethality in the mutant that lacks Dut and RecA and why is this lethality suppressed by loss of Ung?
Hints: Think about the function of each of the proteins and the consequences of their loss. Also look at the first slide from lecture 20.