Figure 7. Insertion of repeat sequences upstream of URA3 increases the mutation rate to Ura−.

12-nucleotide insertions were engineered four base pairs upstream of URA3. Mutation rates of different insertions were determined by fluctuation test using at least 10 cultures. Data represent the mean of three repeats. The strain denoted as wt has no insertion and that designated as random has a non-repeat 12-nucleotide insertion (see Materials and Methods for the sequence). Error bars represent 95% confidence intervals. Significance was calculated using t tests, and asterisks indicate p<0.001.