Flagellin is the subunit protein which polymerizes to form the filaments of bacterial flagella. FlaA binds to flagellar assembly factor FliW protein, preventing FliW from binding to CsrA, so that CsrA can then bind flaA mRNA and represses its translation. Heteromer of FlaA and FlaB. Interacts with FliW. Has 2 short flagella probably composed of flagellin B (flaB). The mRNA is localized to the poles of short, probably elongating, cells; mRNA localization is lost in an fliW deletion strain but restored in a csrA-fliW double deletion. Correct localization requires protein translation; mutation of the start codon to prevent translation initiation or a premature stop codon (at position 3) prevents mRNA localization, a stop codon at position 101 leads to partial localization to the cell poles. Belongs to the bacterial flagellin family.