RNA-binding protein Hfq (IPR005001)

Short name: Hfq

Overlapping homologous superfamilies

Family relationships



This entry represents the RNA-binding pleiotropic regulator Hfq, a small, Sm-like protein of bacteria. It helps pair regulatory non-coding RNAs with complementary mRNA target regions. It enhances the elongation of poly(A) tails on mRNA. It appears also to protect RNase E recognition sites (A/U-rich sequences with adjacent stem-loop structures) from cleavage. Being pleiotropic, it differs in some of its activities in different species. Hfq binds the non-coding regulatory RNA DsrA (see Rfam:RF00014) in the few species known to have it: Escherichia coli, Shigella flexneri, Salmonella spp. In Azorhizobium caulinodans, an hfq mutant is unable to express nifA, and Hfq is called NrfA, for nif regulatory factor (see PMID: 8197116). The name Hfq reflects phenomenology as a host factor for phage Q-beta RNA replication.

The Hfq protein is conserved in a wide range of bacteria and varies in length from 70 to 100 amino acids. In all cases, a conserved Sm motif is located in the N-terminal halves of the molecules. The Hfq protein of E. coli is an 11 kDa polypeptide that forms a hexameric ring-shaped structure. Structural studies have suggested that the beta-4 strand in one molecule dimerises with the beta-5 strand of a neighbouring subunit to form the hexamer. These two strands move with a concerted mobility which may explain the stability of the entire structure [PMID: 12095248].

The architecture of the Hfq-RNA complex suggests two, not mutually exclusive, mechanisms by which Hfq might exert its function as modulator of RNA-RNA interactions. First, when Hfq binds single-stranded RNA, the target site is unwound in a circular manner. This would greatly destabilise surrounding RNA structures that are located several nucleotides on either side of the binding site, thereby permitting new RNA-RNA interactions. Secondly, the repetition of identical BPs on the Hfq hexamer implies that the binding surface can accommodate more than just a single RNA target. This would allow simultaneous binding of two RNA strands and could greatly enhance interaction between the strands [PMID: 15009882].

GO terms

Biological Process

GO:0006355 regulation of transcription, DNA-templated

Molecular Function

GO:0003723 RNA binding

Cellular Component

No terms assigned in this category.

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.