The Acinetobacter baylyi Hfq gene encodes a large protein with an unusual C terminus

In gammaproteobacteria the Hfq protein shows a great variation in size, especially in its C-terminal part. Extremely large Hfq proteins consisting of almost 200 amino acid residues and more are found within the gammaproteobacterial family Moraxellaceae. The difference in size compared to other Hfq proteins is due to a glycine-rich domain near the C-terminal end of the protein. Acinetobacter baylyi, a nonpathogenic soil bacterium and member of the Moraxellaceae encodes a large 174-amino-acid Hfq homologue containing the unique and repetitive amino acid pattern GGGFGGQ within the glycine-rich domain. Despite the presence of the C-terminal extension, A. baylyi Hfq complemented an Escherichia coli hfq mutant in vivo. By using polyclonal anti-Hfq antibodies, we detected the large A. baylyi Hfq that corresponds to its annotated size indicating the expression and stability of the full protein. Deletion of the complete A. baylyi hfq open reading frame resulted in severe reduction of growth. In addition, a deletion or overexpression of Hfq was accompanied by the loss of cell chain assembly. The glycine-rich domain was not responsible for growth and cell phenotypes. hfq gene localization in A. baylyi is strictly conserved within the mutL-miaA-hfq operon, and we show that hfq expression starts within the preceding miaA gene or further upstream.