Table 2 . Characterization of purified subclones from 44 revertants appearing on day 6.
| Genotypes of isolated subclones (total 44) | Mutation(s) in purified subclone | Composition of original revertant colonya | ||||
|---|---|---|---|---|---|---|
| purR | purO | Stem | First mutation | Second mutation | Number of revertants | |
| Single purO (1) | + | − | + | purO | mDEL1b | 1 |
| Single purR (5) | − | + | + | purR | mDEL1 | 5 |
| Single mDEL1 (22) | + | + | Δ | mDEL1 | purO | 1 |
| purR | 7 | |||||
| Extended deletions mDEL3 and mDEL4 | 2 | |||||
| Amplificationc | 12 | |||||
| purO, mDEL1 (3) | + | − | Δ | mDEL1 | purO | 3 |
| purO | mDEL1 | 0 | ||||
| purR, mDEL1 (13) | − | + | Δ | mDEL1 | purR | 4 |
| purR | mDEL1 | 9 | ||||
a
When single cells from a revertant colony are plated on rich medium containing X-gal, they form colonies that are either light blue (if the cell has only one mutation) or dark blue (if the cell has both a regulatory mutation and a stem deletion).
b
The end points of mDEL deletions (1–4) are described in Figure 4.
c
The amplified unit is the chromosomal region between the rrnB and rrnE loci, which includes the purHD operon.