TABLE 3.
Activity of the three lac operon proteins
| Strain | LacZ activity ± SE | LacY activity ± SEa | LacA activity ± SE (×10−3) |
|---|---|---|---|
| On glucose | |||
| lacI+ (DMS267) | 0 | — | 1.004 ± 0.100 |
| lacI− (DMS269) | 2.022 ± 0.057 | 0.1238 ± 0.0050 | 6.173 ± 0.3369 |
| lacI− ΔlacY (DMS1333) | 1.082 ± 0.046 | 0 | 5.146 ± 0.300 |
| lacI− ΔlacZ (DMS1346) | 0 | —b | 3.956 ± 0.104 |
| lacI− ΔRBS (DMS1360) | 0.0279 ± 0.002 | — | 0.955 ± 0.676 |
| lacI−lacZ·ssrA (DMS1397) | 1.236 ± 0.038 | 0.1161 ± 0.0009 | 4.990 ± 0.249 |
| lacI− (DMS269) on | |||
| Succinate | 2.791 ± 0.193 | 0.1321 ± 0.0034 | 5.369 ± 1.075 |
| Maltose | 1.953 ± 0.038 | 0.1576 ± 0.0122 | 7.088 ± 0.135 |
| Melibiose | 2.016 ± 0.123 | 0.1831 ± 0.0082 | 7.553 ± 0.322 |
a
LacY activity as measured by ONPG transport. Strains with negligible LacZ activity (DMS267, DMS1346, and DMS1360) could not be measured by this method.
b
While LacY activity could not be measured by ONPG transport in this strain, α-PNPG transport shows that DMS1346 and DMS269 have the same levels of permease (Figure 1).