Читать книгу Cell Biology - Stephen R. Bolsover - Страница 114

1 The bacteriophage PBS2 is very unusual in that its DNA uses uracil in place of thymine and therefore runs the risk of being “corrected” by the deamination enzymes of the bacterium that it infects. It therefore injects an inhibitor of bacterial uracil DNA glycosidase to prevent this from happening. Consider a section of the bacterial chromosome with the structure and suppose that at around the same time that it is infected by PBS2 a deamination event converts the cytosine to a uracil. Given that with uracil DNA glycosidase deactivated the bacterium cannot repair the error by base excision repair, can it repair the error using mismatch repair enzymes? If the error is not corrected, suggest what will happen to the DNA sequence (i) when the bacterium replicates its DNA and generates two daughter cells (ii) when these cells replicate their DNA to generate four second generation cells?