In addition, the precise role of FliH in flagellar protein secretion is not presently understood. A recent study examining the motility of bacteria with mutant flagellar proteins found that FliI-null mutants are non-motile, FliH-null mutants are weakly motile, and, interestingly, that FliI/FliH double mutants displayed greater (but still impaired) motility than FliI-null mutants after extended incubation [20]. Motivated by

the realization that the mode check details of interaction between FliI and FliH is strikingly similar to that of the N-terminal α-helix of the F1 ATPase α-subunit with the globular domain of the F1 ATPase δ-subunit [18], we have previously suggested that FliH may function as a molecular stator in combination with FliI during the export of flagellum components [18]. In support of this idea, we and other researchers have noted weak but significant sequence similarity between FliH/YscL and the b-subunit of FoF1 ATPases ([7, 21]; S. Moore, unpublished results). AZD9668 clinical trial Figure 1 Primary Sequence of FliH and YscL -

schematic representation of domain organization in FliH and YscL proteins. A flagellum specific region at the N-terminus of FliH which has no correspondence to YscL is shown in gold. An N-terminal YscL-unique segment is shown in green and labelled I. The glycine rich segments described in the text are coloured gold and labelled Gly. The green segment labelled II corresponds to a segment in FliH and YscL homologues found to be similar to the F1 ATPase b-subunits [21]. The red segment labelled III is unique to FliH and YscL. The orange segment labelled δ-C is proposed by Pallen and co-workers to be homologous to the delta subunit (AtpF) of F1 ATPase [21]. Figure 2 Primary Sequence of FliH and YscL – alignment of the N-terminal sequences of FliH from a number of bacterial groups that exhibit weak conservation of primary sequence. The unrelated segment at the N-terminus of YscL is shown for comparison. Figure 3 Primary Sequence of FliH and YscL – multiple alignment of the C-terminal ADP ribosylation factor conserved region of FliH and YscL showing the position of the AxxxG(xxxG) m xxxA repeats for

some representative sequences. Coloured bars relate the sequence segments denoted as II (green), III (red) and δ-C described in Figure 1. Secondary structure prediction for the globular domain at the C-terminus of FliH/YscL is shown as arrows and cylinders for beta strands and alpha helices respectively. Predictions calculated using [35–39]. The present study investigates a conserved GxxxG (where “”x”" represents any amino acid) sequence motif unique to the flagellar FliH/YscL family of proteins. Naming conventions for YscL-like proteins are rather inconsistent, as this protein often has different names in different organisms; for ease of reference, all YscL-like proteins will be referred to in this paper simply as “”YscL”".