Fig. 5.

Role of RNR gene copy numbers for ability to grow in HU, but not in CSP. Strains with different numbers of alleles of RNR1, RNR21, and RNR22 were constructed by one of two strategies: (A) by deletion of one gene copy from diploid strain SC5314, followed by chromosome duplication via exposure to HU or CSP or (B) by deletion of one gene copy from a Chr2 trisomic strain. Strains were spotted (3 µl/spot, 10-fold dilutions) onto HU or CSP plates and incubated at 37 °C for 48 h. All strains in (A) and in (B) were analyzed on the same drug plates. Comparison of mutant growth should be made between euploid strains or between trisomic strains. For example, the Chr2x3 strain (FY376) is a control for all strains in (A) and (B).