Cellular electron microscopy imaging reveals the localization of the Hfq protein close to the bacterial membrane.

BACKGROUND: Hfq is a bacterial protein involved in several aspects of nucleic acid transactions, but one of its best-characterized functions is to affect the post-transcriptional regulation of mRNA by virtue of its interactions with stress-related small regulatory (sRNA). METHODOLOGY AND PRINCIPAL FINDING: By using cellular imaging based on the metallothionein clonable tag for electron microscopy, we demonstrate here that in addition to its localization in the cytoplasm and in the nucleoid, a significant amount of Hfq protein is located at the cell periphery. Simultaneous immunogold detection of specific markers strongly suggests that peripheral Hfq is close to the bacterial membrane. Because sRNAs regulate the synthesis of several membrane proteins, our result implies that the sRNA- and Hfq-dependent translational regulation of these proteins takes place in the cytoplasmic region underlying the membrane. CONCLUSIONS: This finding supports the proposal that RNA processing and translational machineries dedicated to membrane protein translation may often be located in close proximity to the membrane of the bacterial cell.