Figure 5.

Putative σ^28† mutants exhibit weak σ²⁸* activity. β-Galactosidase activity of a fliC-lacZ transcriptional fusion (fliC5050::MudJ) in various flagellar mutant backgrounds. The activities of σ²⁸ mutants were compared with σ²⁸⁺, flgM ⁻, σ²⁸*[H14D] (increased-stability σ²⁸ with wild-type FlgM-binding), and σ²⁸*[V213E] (severe FlgM binding defective σ²⁸) in strains with either a HBB⁺ (white bars) or HBB⁻ (black bars) phenotype. Surprisingly, even though σ²⁸*[V33E], σ²⁸*[G77W L135S], σ²⁸*[E193V], σ²⁸*[S226R], and σ²⁸*[E209G V221A] all exhibited lower σ²⁸ transcriptional activity for HBB⁺ strains compared with HBB⁺ σ²⁸⁺, they all showed a weak σ²⁸* phenotype in the HBB⁻ strains. In contrast, significant increases in fliC-lacZ transcription for both HBB⁺ and HBB⁻ strains were observed for the σ²⁸*[H14D] and σ²⁸*[V213E] mutants. A complete description of the genotypes of all HBB⁺ strains used in this analysis is to be found in Table 3. HBB⁻ strains were constructed by transduction of the flgG574::Tn10 allele.