title: Functional Activation of the Flagellar Type III Secretion Export Apparatus.
abstract: Flagella are assembled sequentially from the inside-out with morphogenetic checkpoints that enforce the temporal order of subunit addition. Here we show that flagellar basal bodies fail to proceed to hook assembly at high frequency in the absence of the monotopic protein SwrB of Bacillus subtilis. Genetic suppressor analysis indicates that SwrB activates the flagellar type III secretion export apparatus by the membrane protein FliP. Furthermore, mutants defective in the flagellar C-ring phenocopy the absence of SwrB for reduced hook frequency and C-ring defects may be bypassed either by SwrB overexpression or by a gain-of-function allele in the polymerization domain of FliG. We conclude that SwrB enhances the probability that the flagellar basal body adopts a conformation proficient for secretion to ensure that rod and hook subunits are not secreted in the absence of a suitable platform on which to polymerize.
authors.affiliation: Department of Biology, Indiana University, Bloomington, Indiana, United States of America.
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Phillips
authors.affiliation: Department of Biology, Indiana University, Bloomington, Indiana, United States of America.
authors.forename: Rebecca A
authors.initials: RA
authors.lastname: Calvo
authors.affiliation: Department of Biology, Indiana University, Bloomington, Indiana, United States of America.
authors.forename: Daniel B
authors.initials: DB
authors.lastname: Kearns
mesh_terms: D000483:Alleles; D001412:Bacillus subtilis / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D015870:Gene Expression; D005798:Genes, Bacterial; D009876:Operon; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D000069296:Type III Secretion Systems / Q000502:physiology*
chemical_list: D000069296:Type III Secretion Systems