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==History==

Hfq was first identified in the lates 1960s in Escherichia coli as a essential host factor for the RNA replication of the bacteriophage Qβ. Later, in the 1990s, was shown that Hfq could provide greatest benefits to the bacterium itself, rather than to its phage predator. Tsui and colleagues, in 1994, described a diverse of pleiotropic effects caused by the disruption of the hfq gene, related to fitness reduce, stress response impairment and, in pathogenic bacterias, diminishment of virulence.

==Function==

Hfq is a bacterial post-transcriptional regulator that modulates RNA structure, acting as a RNA chaperone. The most well-characterized function of Hfq is its role as a RNA matchmaker, promoting interactions between small non-coding RNAs (sRNAs) and messenger RNAs (mRNAs), leading translation and RNA stability regulation. There are several mechanisms to Hfq-mediated regulation. Most of the Hfq/RNAs/RNAm interactions described report inhibition of translation, although there are cases of positive regulation (Santos et al., 2019). Hfq can suppress protein synthesis by aiding the sRNA to bind the 5’ region of its target mRNA turning this region inaccessible to translation initiation. In the other way, this RNA chaperone can also act boosting translation, where sRNA guided by Hfq can bind in the 5’ region of the mRNA, changing its structure that otherwise inhibits ribosome binding. Hfq can also present a sRNA to its mRNA target leading to both degradation (Vogel & Luisi, 2011).

It also has been shown that Hfq can interacts with either RNAs or RNAm independently, not just between this molecules. Hfq can modulate mRNA stability by directly binding and remodeling without the sRNA. It can also promotes the polyadenylation at the 3’ end of mRNAs, which in turn triggers 3’ to 5’ degradation by a exoribonuclease. The Hfq association also protects sRNAs from degradative activity of polynucleotide phosphorylase (PNPase) and ribonuclease E (RNase E) (Vogel & Luisi, 2011; Santos et al., 2019).

Hfq is able to bind ATP, however, the chaperoning activity does not require ATP hydrolysis (Santos et al., 2019).

Recently, the discovery of others binding substrates with Hfq has expanded the regulatory spectrum of this protein. It was found that this RNA chaperone can also bind with rRNA, tRNA and DNA. Studies have shown that Hfq promotes ribosome assembly in bacteria, where this protein is required for the processing of pre-16S and folding of the mature 16S rRNA in E. coli, displaying Hfq as a important ribosome biogenesis factor in bacterias. This process seems to be independent of Hfq interactions with sRNAs, which the binding surfaces of the vast majority of the Hfq-dependent sRNAs are the proximal and rim faces, and for the rRNA, in the distal face of the Hfq. The same was observed for tRNA, where Hfq was also associated as a important pre-tRNA maturation factor, however, the binding of the structural elements of tRNAs occurs through the proximal face of Hfq.

Notably, the regulatory activity of Hfq is not restricted to RNAs, it was also found to bind DNA, acting as a important factor in chromosome structure. Hfq was found to form a fiber like structure that leads, indirectly, to chromosome compaction through a mechanism still elusive. It is also associated with regulation of cellular replication and transfer of several transposon systems (Santos et al., 2019).

==Structure Highlights==

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 <Structure load='1KQ2' size='350' frame='true' align='right' caption='Insert caption here' scene='Insert optional scene name here' />
+==History==
+Hfq was first identified in the lates 1960s in Escherichia coli as a essential host factor for the RNA replication of the bacteriophage Qβ. Later, in the 1990s, was shown that Hfq could provide greatest benefits to the bacterium itself, rather than to its phage predator. Tsui and colleagues, in 1994, described a diverse of pleiotropic effects caused by the disruption of the hfq gene, related to fitness reduce, stress response impairment and, in pathogenic bacterias, diminishment of virulence.
+==Function==
+Hfq is a bacterial post-transcriptional regulator that modulates RNA structure, acting as a RNA chaperone. The most well-characterized function of Hfq is its role as a RNA matchmaker, promoting interactions between small non-coding RNAs (sRNAs) and messenger RNAs (mRNAs), leading translation and RNA stability regulation. There are several mechanisms to Hfq-mediated regulation. Most of the Hfq/RNAs/RNAm interactions described report inhibition of translation, although there are cases of positive regulation (Santos et al., 2019). Hfq can suppress protein synthesis by aiding the sRNA to bind the 5’ region of its target mRNA turning this region inaccessible to translation initiation. In the other way, this RNA chaperone can also act boosting translation, where sRNA guided by Hfq can bind in the 5’ region of the mRNA, changing its structure that otherwise inhibits ribosome binding. Hfq can also present a sRNA to its mRNA target leading to both degradation (Vogel & Luisi, 2011).
+It also has been shown that Hfq can interacts with either RNAs or RNAm independently, not just between this molecules. Hfq can modulate mRNA stability by directly binding and remodeling without the sRNA. It can also promotes the polyadenylation at the 3’ end of mRNAs, which in turn triggers 3’ to 5’ degradation by a exoribonuclease. The Hfq association also protects sRNAs from degradative activity of polynucleotide phosphorylase (PNPase) and ribonuclease E (RNase E) (Vogel & Luisi, 2011; Santos et al., 2019).
+Hfq is able to bind ATP, however, the chaperoning activity does not require ATP hydrolysis (Santos et al., 2019).
+Recently, the discovery of others binding substrates with Hfq has expanded the regulatory spectrum of this protein. It was found that this RNA chaperone can also bind with rRNA, tRNA and DNA. Studies have shown that Hfq promotes ribosome assembly in bacteria, where this protein is required for the processing of pre-16S and folding of the mature 16S rRNA in E. coli, displaying Hfq as a important ribosome biogenesis factor in bacterias. This process seems to be independent of Hfq interactions with sRNAs, which the binding surfaces of the vast majority of the Hfq-dependent sRNAs are the proximal and rim faces, and for the rRNA, in the distal face of the Hfq. The same was observed for tRNA, where Hfq was also associated as a important pre-tRNA maturation factor, however, the binding of the structural elements of tRNAs occurs through the proximal face of Hfq.
+Notably, the regulatory activity of Hfq is not restricted to RNAs, it was also found to bind DNA, acting as a important factor in chromosome structure. Hfq was found to form a fiber like structure that leads, indirectly, to chromosome compaction through a mechanism still elusive. It is also associated with regulation of cellular replication and transfer of several transposon systems (Santos et al., 2019).
 ==Structure Highlights==