Figure 4.

Reduction in histone gene dosage affects the efficiency of DSB repair by the HR but not the NHEJ pathway. (a) Survival of strains lacking the HMRa and HMLα donor sequences on GAL-HO-mediated DSB induction. Tenfold serial dilutions of the indicated GAL-HO strains carrying deletions of hml and hmr sequences were plated to determine their relative viability on glucose and galactose media. The plates were incubated for 4 days at 30°C before being photographed. (b) Quantitation of the survival of strains lacking the HMRa and HMLα donor sequences following a DSB created by HO endonuclease. Quantitative representation of the result shown in (a) exactly as described for Figure 3b. (c) Plasmid recircularization assay for NHEJ. Equal amounts of HindIII linearized or uncut supercoiled plasmids carrying a Kan^R marker for G418 resistance were transformed into the same number of yeast cells from each strain and plated on media containing the selection antibiotic G418. Viable colonies were counted and normalized to wild-type cells transformed with uncut supercoiled plasmid. The error bars represent standard error of the mean from three independent repeats of the experiments under identical conditions.