FIG 6.

Signaling and adaptational modification properties of Tsr control cable mutants. (A) Serine response sensitivities of cells carrying mutant Tsr plasmids (data from Tables 1, 2, and 3) in host strains UU2567 (R⁻ B⁻; diamonds) and UU2700 (R⁺ B⁺; arrowheads). Broken black arrows indicate incomplete adaptation to a serine stimulus at the K_1/2 concentration for that receptor. Broken gray arrows indicate partial, methylation-independent adaptation to a K_1/2 concentration serine stimulus. The white arrow indicates no discernible adaptation to a K_1/2 concentration serine stimulus. NR-OFF, no response and no kinase activity; NR-ON, no response and high kinase activity. Horizontal lines indicate the corresponding K_1/2 values for wild-type Tsr (19 μM in UU2567; ∼0.5 μM in UU2700). Phenotypic signaling classes are listed at the bottom. (B) Adaptational modification of receptor subunits in various host strains. This summary is based on SDS-PAGE analyses of mutant Tsr proteins and the mobilities of their methylated forms relative to their Q-state counterparts (see Fig. S4 and S5 in the supplemental material; and data from reference 12). Diamonds indicate the 2-Q (QEQEE) state in UU2610 (R⁻ B⁻). Arrowheads indicate predominant modification states in hosts with one or both adaptation enzymes: R⁻ B⁺ (UU2611; light gray arrows), R⁺ B⁻ (UU2632; dark gray arrows), and R⁺ B⁺ (UU2612; black arrows). White diamonds indicate that the majority of subunits are shifted from the 2-Q state in a particular host. Black diamonds indicate that the majority of subunits remain at the 2-Q position in a particular host. Thick arrows indicate major-modification species; thin arrows indicate minor extents of modification. Broken arrows indicate modification changes elicited by a saturating serine stimulus.