Minimum amino acid substitutions required to confer the TS phenotype. NMB190 cells expressing no PomA (vector), wild-type PomA (WT), and the PomA mutants (PomA-R88A, PomA-E96Q, PomA-R88A/E96Q, AAQQQ PomA, PomA-R88A+L131F, PomA-E96Q+L131F, PomA-R88A/E96Q+L131F, or AAQQQ+L131F PomA) were grown at 20°C (for 10 h), 30°C (for 5 h), 37°C (for 3.5 h), and 42°C (for 3.5 h).