2. Haploid yeast cells that preferentially repair double-strand breaks by homologous recombination are especially sensitive to agents that cause double-strand breaks in DNA. If the breaks occur in the G1 phase of the cell cycle (before DNA replication), most yeast cells die; however, if the breaks occur in the G2 phase (after DNA replication), a much higher fraction of cells survive.

(a) What are the key proteins required for homologous recombination in yeast (a eukaryote)?

(b) Yeast can also carry out repairs by non-homologous end-joining (NHEJ). How does this form of repair different from repair of double-strand DNA breaks by homologous recombination?

(c) Explain the observations described above.